Search

Presented here is a solid-state NMR investigation of the so-called 'colossal expansion' material, [Ag.sub.3]Co[(CN).sub.6], a compound that exhibits some of the largest positive and negative thermal expansion properties reported. This study explores the [sup.13]C, [sup.15]N, and [sup.59]Co NMR properties of this material at room temperature and at variable temperatures with the goal of probing the effects of this colossal expansion behaviour on these properties. We found that the flexible nature of the crystal framework leads to a distribution of electric field gradients, and that, oddly enough, no strong correlation is observed between the NMR parameters of [Ag.sub.3]Co[(CN).sub.6] and its colossal expansion nature. The [sup.59]Co isotropic chemical shift increased and the [sup.59]Co nuclear quadrupolar coupling constant decreased with increasing temperature, but neither of these relationships were extraordinary when compared to other octahedral Co(III) complexes. The link between the colossal expansion and the NMR properties of [Ag.sub.3]Co[(CN).sub.6] may be the distribution of lattice parameters and hence unusually broad features in the [sup.59]Co NMR spectra. The high order of symmetry at the cobalt site resulted in a small quadrupolar coupling constant less than 1 MHz in magnitude. We also observed a [absolute value of ¹J([sup.107/109]Ag,[sup.15]N)] value of 96 Hz, the largest [sup.107/109]Ag-[sup.15]N coupling constant reported to date. Key words: colossal expansion material, solid-state NMR, Co-59 NMR, C-13 NMR, N-15 NMR. Dans ce travail, on rapporte les resultats d'une etude RMN a l'etat solide du materiau dit d'<< expansion colossale >>, [Ag.sub.3]Co[(CN).sub.6], un compose qui possede des proprietes d'expansion thermique positives et negatives parmi les plus grandes. Cette etude examine les proprietes RMN du [sup.13]C, du [sup.15]N et du [sup.59]Co, a la temperature ambiante ainsi qu'a des temperatures variables, dans le but d'etudier les effets de ce comportement d'expansion colossale sur ces proprietes. On a trouve que la nature flexible du reseau cristallin conduit a une distribution des gradients des champs electriques et que, d'une facon surprenante, il n'existe aucune correlation forte entre les parametres RMN du [Ag.sub.3]Co[(CN).sub.6] et sa nature d'expansion colossale. Le deplacement chimique isotrope du [sup.59]Co augmente alors que la constante de couplage quadripolaire nucleaire du [sup.59]Co diminue avec une augmentation de la temperature; aucune de ces relations n' est toutefois extraordinaire quand on les compare avec celles d'autres complexes octaedriques du Co(III). Le lien entre l'expansion colossale et les proprietes RMN du [Ag.sub.3]Co[(CN).sub.6] pourrait provenir de la distribution des parametres de reseaux et, en consequence, de caracteristiques anormalement larges dans les spectres RMN du [sup.59]Co. Le degre de symetrie eleve au niveau du site du cobalt conduit a une constante de couplage quadripolaire faible, dont l'amplitude est inferieure a 1 Mhz. On a aussi observe une valeur [absolute value of ¹J([sup.107/109]Ag,[sup.15]N)] de 96 Hz, la constante de couplage la plus grande observee jusqu'a maintenant pour [sup.107/109]Ag,[sup.15]N. Mots-cles: materiau d'expansion colossale, RMN a l'etat solide, RMN du Co-59, RMN du C-13, RMN du N-15. [Traduit par la Redaction], Introduction In 2008, Goodwin et al. (1) reported that silver hexacyanocobaltate(III), [Ag.sub.3]Co[(CN).sub.6], exhibits the highest known relative positive and negative thermal crystal framework expansion. The structure of this material has [...]

We present a diffraction analysis for image formation in fluorescence confocal microscopy with divided apertures. The three-dimensional optical transform function is given, and axial resolution and transverse resolution are investigated. The results show that the employment of a divided-aperture technique in fluorescence confocal microscopy can enhance the rejection of background scattering. In addition, the axial resolution and transverse resolution can be improved by adjusting the width of the divider strip. For a given detector size, an optimum value of the divider strip width is given to obtain the best axial resolution or transverse resolution. The integrated intensity and signal-to-background ratio are also discussed. [c] 2010 Optical Society of America OCIS codes: 170.3660, 170.4580, 170.6510, 170.1530, 290.0290.

A theoretical approach based on coupled-mode theory is described in order to determine the radiation pattern of LEDs incorporating a shallow photonic crystal, thereby providing a fundamental limit for the directionality of the diffraction of the single guided mode. The Fabry-Perot resonances have a major impact on the directionality of diffracted light and the spontaneous emission distribution between guided modes has affected the diffracted intensity.

The article discusses the design and properties of a highly efficient quasi-optical mode converter, which exhibit s a bandwidth of 38 GHz and is used for the multifrequency high-power gyrotron. The converter is shown to be extremely beneficial, as it exhibit well-focused Gaussian beam at all the operating modes.

Waveguide based 1-D photonic crystal (PC) microcavities in silicon-on-insulator are examined by 2-D finite-difference time-domain method. A new tapered structure with varying Si block width has shown an ultrahigh-Q and has relieved the fabrication constraints when compared to the conventional air slots tapered structure.

An approximation Phase Corrected Scattering Integral (PCSI) method to evaluate the acoustic field within tissue is described. The PCSI method is able to deal very effectively with scattering due to small changes in sound speed and irregular geometry which are characteristic of biomedical problems.

We present an efficient algorithm for the tracing of multiply edge diffracted rays. The algorithm assumes a given sequence of infinite edges and complete visibility among them. The ray tracing problem is formulated as the minimization of the ray total path length. Since such a cost function is strictly convex, except for coplanar edges in the plane-wave far-field regime, then the problem admits a unique global minimum and allows the use of a modified Newton search algorithm, which exhibits a very high converging rate. We also propose a convenient starting point to effectively initialize the minimization algorithm. The proposed algorithm is tested by some numerical examples that show its efficiency and effectiveness. Index Terms--Electromagnetic propagation, multiple diffraction, ray tracing, uniform theory of diffraction (UTD).

An analysis for diffraction of sound by a fluid cylinder of elliptic cross section suspended in a Newtonian (viscous) fluid medium is presented. The study offers insight into the influence of the cylinder's cross-sectional ellipticity in addition to the viscous fluid effects on acoustic scattering, which increases on increasing the frequency in both viscous and ideal fluid situations.

The structure solution, model building and refinement of a biologically important second SH3 (Src homology -3) domain of ponsin are described by using high-angular-resolution powder diffraction. The results have shown the power and future applicability of the powder technique in structural biology.

The design and synthesis of A[B.sub.4] and A[B.sub.5] dendritic building blocks with complex architecture are described. They has self-assembled into spherical dendrimers with a less densely packed center and the long-range helical structures are established by applying the helical diffraction theory of the analysis of X-ray patterns obtained from oriented fibers of supramolecular dendrimers.

The article describes a method for ultrasonic synthetic aperture imaging using finite-sized transducers introduced, which is based on a virtual source (VS) concept.

Subwavelength metallic and dielectric diffraction gratings which rotate the linear polarization of incident light by 90[degrees] are examined. Using rigorous diffraction theory in total-internal-reflection configuration, it is shown that full conversion from incident transverse electric field to transverse magnetic zero-order field can be achieved with both dielectric and metallic elements, but dielectric gratings provide higher efficiency and are thus preferable. The fabrication aspects and constraints are discussed in detail and the behavior of the gratings over broad wavelength bands is presented. OCIS codes: 230.1950, 260.2110, 260.5430.

The model analyses the 2-D surface-emitting active-photonic crystal (APC) lasers that combines a resonant-optical-waveguide (ROW) and distributed feedback Bragg reflector (DFB) semiconductor gratings.

The articles studies on the development of extended high frame rate (HFR) imaging method which better image quality and frame rate and motion artifacts for using it in various applications.

An axial superresolution diffraction theory is developed in a two-photon microfabrication system. This method can improve the axial superresolution of the two-photon microfabrication system. A theoretical analysis of the photosensitive resin is discussed based on the exciting power and the concentration of free radical theory. Simulated results of the two-photon microfabrication verify the method and show that it can provide insight into the microfabrication system. OCIS codes: 220.4000, 220.4610, 220.4830, 220.4840.

We present a fast algorithm for path computation of multiple diffracted rays relevant to ray tracing techniques. The focus is on double diffracted rays, but generalizations are also mentioned. The novelty of our approach is in the use of an analytical geometry procedure which permits to re-write the problem as a simple nonlinear equation. This procedure permits a convergence analysis of the algorithms involved in the numerical resolution of such nonlinear equation. Moreover, we also indicate how to choose the iteration starting point to obtain convergence of the (locally convergent) Newton method. As in previous works, explicit solutions are obtained in the relevant cases of parallel or incident diffraction edges. Index Terms--Electromagnetic edge diffraction, HF wave propagation, multiple diffraction, Newton method, ray tracing, urban propagation.

Computer simulations of nanofocusing by elliptical mirrors are presented wherein the diffraction and propagation of coherent hard x rays are predicted using wave-optical calculations. Surface height data acquired via microstitching interferometry were used to calculate the complex pupil function of a mirror, taking into account the Fresnel refiectivity and treating the surface topography as an aberration to a perfect elliptical mirror. The reflected wave-field amplitude and phase downstream of the mirror were obtained by numerically evaluating the Fresnel-Kirchhoff diffraction integral. Simulated intensity profiles and contours (isophotes) around the focal plane are presented for coherent illumination by a 15 keV point source, which indicate nearly difffraction-limited focusing at the 40 nm level. The effect of high spatial frequency microroughness on nanofocusing was investigated by low-pass filtering the Fourier spectrum of the residual height profile. Simulations using the filtered metrology data confirmed that roughness length scales shorter than 0.1 mm have a minor effect on the focal spot size and intensity. OCIS codes: 260.0260, 120.5700, 120.6660, 340.7470.

This paper presents novel heuristic coefficients for the uniform theory of diffraction (UTD), suited to analyze the scattering by lossy conducting wedges in an efficient and reciprocal manner. For its reciprocal properties, the coefficients are appropriate to handle complex scenarios with arbitrary transmitter and receiver positions. The new coefficients take advantage of two previously proposed heuristic coefficients, combining both in a novel approach. The diffraction by arbitrary conducting wedges is investigated and results are compared with those given by accurate Maliuzhinets and method-of-moments analyses. The proposed technique is then applied to characterize the scattering through a typical urban scenario in order to demonstrate its applicability. Index Terms--Heuristic diffraction coefficients, scattering by lossy wedges, uniform theory of diffraction (UTD).

High-energy petawatt lasers use series of spatial filters in their amplification section. The refractive lenses employed introduce longitudinal chromatism that can spatially and temporally distort the ultrafast laser beam after focusing. To ensure optimum performances of petawatt laser facilities, these distortions need to be corrected. Several solutions using reflective, refractive, or diffractive optical components can be addressed. We give herein a review of these various possibilities with their application to the PETAL (Petawatt Aquitaine Laser at the Laser Integration Line facility) laser beamline and show that diffractive-based corrections appear to be the most promising. OCIS codes: 140.7090, 050.5080.

We have developed a parallel algorithm for microdigital-holographic particle-tracking velocimetry. The algorithm is used in (1) numerical reconstruction of a particle image computer using a digital hologram, and (2) searching for particles. The numerical reconstruction from the digital hologram makes use of the Fresnel diffraction equation and the FFT (fast Fourier transform), whereas the particle search algorithm looks for local maximum graduation in a reconstruction field represented by a 3D matrix. To achieve high performance computing for both calculations (reconstruction and particle search), two memory partitions are allocated to the 3D matrix. In this matrix, the reconstruction part consists of horizontally placed 2D memory partitions on the x-y plane for the FFT, whereas, the particle search part consists of vertically placed 2D memory partitions set along the z axes. Consequently, the scalability can be obtained for the proportion of processor elements, where the benchmarks are carried out for parallel computation by a SGI Altix machine. OCIS codes: 090.1760, 120.7250.

The similarities and differences between two types of surface waves that can exist on a plane metal-lossless dielectric interface, on the one hand, and on a plane lossy-lossless dielectric interface, on the other hand, are analyzed numerically. They both can lead to total absorption of light by surface relief gratings and show different behavior in transmission by lamellar gratings. OCIS codes: 050.1950, 050.1960.

The fabrication of nanoscale aperture arrays in metallic coatings on optical fibers is described. The results from the optical fibers are compared with larger array areas fabricated on bulk glass substrates, which are further simulated by using near- and intermediate-field diffraction theory.

We present experimental results on the intracavity generation of radially polarized light by incorporation of a polarization-selective mirror in a C[O.sub.2]-1aser resonator. The selectivity is achieved with a simple binary dielectric diffraction grating etched in the backsurface of the mirror substrate. Very high polarization selectivity was achieved, and good agreement of simulation and experimental results is shown. The overall radial polarization purity of the generated laser beam was found to be higher than 90%.

We present the analysis and design of a new type of photonic crystal (PC) demultiplexers (i.e., preconditioned demultiplexer), in which the simultaneous existence of the superprism effect and the negative effective index for diffraction results in a compact structure by canceling the second-order spectral phase to avoid beam broadening inside the PC. This approach considerably relaxes the requirements for the large area of the structure and the small divergence of the input beam. As a result, the size of the preconditioned demultiplexers varies as [N.sup.2.5] (N being the number of wavelength channels) compared to the [N.sup.4] variation in the conventional superprism-based PC demultiplexers. We use a generalized effective index model to analyze, design, and optimize these demultiplexing structures. This approximate model can be used to extract all the basic properties of the PC device simply from the band structure and eliminates the need to go through tedious simulations especially for three-dimensional structures. Our results show that the preconditioned superprism-based PC demultiplexers have 2 orders of magnitude smaller size compared to the conventional ones.