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The kinetics of strain-induced crystallization in natural rubber were studied by synchrotron wide-angle X-ray diffraction (WAXD) in a strain jump setup over a broad temperature range. The increase of crystallinity after a strain jump was observed on a millisecond time scale, until a steady state plateau was approached. A novel model, based on chain dynamics scaling laws for diffusion in polymer networks was developed to interpret the time and temperature dependence of the strain-induced crystallization. In contrast to established thermal crystallization models, this model for the strain-induced crystallization proposes that the formation of stretched crystallizable chain segments takes place before the attachment to a growing crystallite. [ABSTRACT FROM AUTHOR]

We study theoretically the propagation and localization of acoustic waves in quasi-periodic structures made of solid and fluid layers arranged according to a Fibonacci sequence. We consider two types of structures: either a given Fibonacci sequence or a periodic repetition of a given sequence called Fibonacci superlattice. Various properties of these systems such as: the scaling law and the self-similarity of the transmission spectra or the power law behavior of the measure of the energy spectrum have been highlighted for waves of sagittal polarization in normal and oblique incidence. In addition to the allowed modes which propagate along the system, we study surface modes induced by the surface of the Fibonacci superlattice. In comparison with solid–solid layered structures, the solid–fluid systems exhibit transmission zeros which can break the self-similarity behavior in the transmission spectra for a given sequence or induce additional gaps other than Bragg gaps in a periodic structure. [ABSTRACT FROM AUTHOR]

Coherent backscatter enhancement (CBE) is a multiple scattering phenomenon that can lead to a doubling of the backscattered field intensity from a random aggregation of scatterers. It may be useful for remote sensing of scatterer aggregations, such as fish schools. This paper presents simulations of acoustic CBE from randomly placed omnidirectional point scatterers based on Foldy's field equations. The simulations are verified and validated through comparisons with Bragg scattering and Foldy's effective-medium theory, assessments of acoustic energy conservation, and comparisons with prior optical and acoustical CBE results. To make CBE comparisons with prior optics results, a CBE coherence function was postulated to account for resolution differences between the optics and simulation studies. For the higher-resolution optics studies, the postulated coherence function yields a CBE of 1.68, which matches optical CBE measurements. For the lower-resolution simulations, the same coherence function yields a CBE of 1.034, which agrees with appropriately extrapolated CBE simulation results, 1.030 ± 0.005. Assuming comparable resolution, the acoustics experiment and simulations both produce a CBE of approximately 1.5. The CBE peak is found to increase approximately monotonically with (κ²δs1/4(κs)-1, where κ is the wave number, s is the average spacing between scatterers, and δs is a scatterer's cross section. [ABSTRACT FROM AUTHOR]

A new compact Bragg type gas ionization chamber (GIC) has been built for use as particle counter in AMS and IBA applications. The detector stands out due to its simple concept, which does not include a Frisch grid. Test experiments have been performed with ions in the mass range from He to Th and energies ranging from 30 keV to 2.5 MeV, in order to find optimal measurement conditions and to characterize the detector performance. For projectiles heavier than Al at energies below 2.5 MeV the obtained energy resolution is comparable with that of a state-of-the-art GIC with Frisch grid and clearly outperforms solid state detectors. Additionally the operation of this simplified Bragg GIC in the electron multiplication mode was investigated for the first time, which allows the detection of radiocarbon ions at energies below 50 keV with an energy resolution of the order of 10 keV. [ABSTRACT FROM AUTHOR]

A nanocomposite composed of Nb nanosheets and NiTi shape memory alloy was fabricated by multiple cold rolling. High-energy X-ray diffraction measurements were performed to probe the deformation behavior of each component during uniaxial tensile loading at different temperatures. It is demonstrated that, as the samples were tested at 203 K (−70 °C) and 298 K (25 °C), the NiTi matrix exhibited a martensite reorientation and a stress-induced phase transformation, respectively, while the Nb nanosheets showed a higher elastic strain (~2.5 pct) in comparison to that (~0.9 pct) of a sample tested at a higher temperature of 453 K (180 °C). The Nb nanosheets, with a volume fraction of only 13 pct, undertake an applied stress of ~90 pct as the NiTi matrix undergoes the martensitic transformation. It appears that the strengthening of Nb nanosheets is optimized as the matrix deforms by a stress-induced phase transformation or by a martensite reorientation in nanocomposite. [ABSTRACT FROM AUTHOR]

Three series of stable, neutral, π-extended bispentalene derivatives, with two pentalenes fused to a central benzene or naphthalene moiety, have been prepared through a modified double carbopalladation cascade reaction. While these chromophores feature skeletons with [4n+2] π-electron perimeters, the two 8 π-electron pentalene subunits strongly influence bonding and spectral properties. ¹H NMR spectra showed large upfield shifts of the protons in the pentalene moieties, comparable to antiaromatic monobenzopentalenes. Further investigations on magnetic ring currents through NICS-XY-scans suggest a global paratropic current and a local diatropic current at the central benzene ring in two of the series, while the third series, with a central naphthalene ring, showed more localized ring currents, with stronger paratropic ring currents on the pentalene moieties. X-ray diffraction analyses revealed planar bispentalene cores with large double- and single-bond alternation in the pentalene units, characteristic for antiaromaticity, and small alternation in the central aromatic rings. In agreement with TD-DFT calculations, both optical and electrochemical data showed much smaller HOMO--LUMO energy gaps compared to other neutral, acene-like hydrocarbons with the same number of fused rings. Both experimental and computational results suggest that the molecular properties of the presented bispentalenes are dominated by the antiaromatic pentalene-subunits despite the [4n+2] π-electron perimeter of the skeletons. [ABSTRACT FROM AUTHOR]

In solid-state science, most changing phenomena have been mysterious. Furthermore, the changes in chemical composition should be added to mere physical changes to also cover the chemical changes. Here, the first success in characterizing the nature of gas inclusion in a single crystal is reported. The gas inclusion process has been thoroughly investigated by in situ optical microscopy, single-crystal X-ray diffraction analyses, and gas adsorption measurements. The results demonstrated an inclusion action of a first-order transition behavior induced by a critical concentration on the phase boundary. The transfer of phase boundary and included gas are strongly related. This relationship can generate the dynamic features hidden in the inclusion phenomena, which can lead to the guest capturing and transfer mechanism that can apply to spatiotemporal inclusion applications by using host solids. [ABSTRACT FROM AUTHOR]

A new one-dimensional Zn(II)-cyanide complex with 1-methylimidazole ligand, [Zn(μ-CN)(CN)(1-meim)]n (1-meim: 1-methylimidazole) has been synthesized and characterized by spectral (FT-IR and Raman) methods, elemental analysis, thermal (TG, DTG and DTA) analysis and single crystal X-ray diffraction techniques. The complex crystallizes in the monoclinic system, P2 1 space group. The asymmetric unit contains one Zn(II), one 1-meim and two cyanide ligands. The coordination sphere of the Zn(II) ion exhibits a distorted tetrahedral geometry. In the crystal structure, the symmetry related zinc(II) atoms are bridged by the cyanide anions to form one dimensional chains running along the b-axis. Intermolecular C-H···N hydrogen bonds link the adjacent polynuclear chains forming two dimensional layers through the ring motifs, where the layers formed are oriented in parallel to (020). [ABSTRACT FROM AUTHOR]

Silver nanoparticles capped by poly(vinyl alcohol) (AgNP@PVA) was prepared by reduction of AgNO in aqueous solution of PVA with the help of catalytic amount of tyrosine as reducing agent, under ultrasonic irradiation. Then, AgNP@PVA were embedded into the l-leucine containing poly(amide-imide) (PAI) matrix via sonication technique to prepare a completely green and environmentally friendly PAI/AgNP@PVA nanocomposites (NCs). The formation of PAI/AgNP@PVA NCs was confirmed by ultraviolet-visible spectroscopy, X-ray diffraction analysis, and Fourier transform infrared techniques. The morphology and thermal stability of the hybrid NCs were examined by field emission scanning electron microscopy (FE-SEM) and thermogravimetric analysis, respectively. The FE-SEM micrographs of PAI/AgNP@PVA NCs showed that AgNP@PVA were well dispersed in the polymer matrix, because Ag NPs had outstanding adhesion and strong interfacial bonding with PAI. [ABSTRACT FROM AUTHOR]

A new one-dimensional Zn(II)-cyanide complex with 1-methylimidazole ligand, [Zn(μ-CN)(CN)(1-meim)]n (1-meim: 1-methylimidazole) has been synthesized and characterized by spectral (FT-IR and Raman) methods, elemental analysis, thermal (TG, DTG and DTA) analysis and single crystal X-ray diffraction techniques. The complex crystallizes in the monoclinic system, P2 1 space group. The asymmetric unit contains one Zn(II), one 1-meim and two cyanide ligands. The coordination sphere of the Zn(II) ion exhibits a distorted tetrahedral geometry. In the crystal structure, the symmetry related zinc(II) atoms are bridged by the cyanide anions to form one dimensional chains running along the b-axis. Intermolecular C-H···N hydrogen bonds link the adjacent polynuclear chains forming two dimensional layers through the ring motifs, where the layers formed are oriented in parallel to (020). [ABSTRACT FROM AUTHOR]

7Li–7Li correlation MAS NMR spectroscopy, interpreted using periodic DFT including molecular dynamics conformational sampling of Li+ sites, is employed to obtain the siting of Li+ at exchangeable positions of ferrierites and the local structure of these Li+ sites. The former is controlled by the Al siting in the zeolite framework. [ABSTRACT FROM AUTHOR]

In this paper, we study the propagation of ultrashort optical pulses, which can be regarded as discrete solitons in this case, when the medium with carbon nanotubes (CNTs), has spatially modulated refractive index. As a result we were able to obtain the effective equation, which represents an analog of the classical sine-Gordon equation. A detailed analysis of the dependence on various parameters of the problem has been performed. [ABSTRACT FROM AUTHOR]

The diffraction of X rays incident on a crystal surface under grazing angles under conditions of total external reflection has been investigated. An approach is proposed in which exact solutions to the dynamic problem of grazing-incidence diffraction in an ideal crystal are used as initial functions to calculate the diffuse component of diffraction in a crystal with defects. The diffuse component of diffraction is calculated for a crystal with surface defects of a dilatation-center type. Exact formulas of the continuum theory which take into account the mirror-image forces are used for defect-induced atomic displacements. Scattering intensity maps near Bragg peaks are constructed for different scan modes, and the conditions for detecting primarily the diffuse component are determined. The results of dynamic calculations of grazing-incidence diffraction in defect-containing crystals are compared with calculations in the kinematic approximation. [ABSTRACT FROM AUTHOR]

We report numerical analyses of Bragg diffraction by Denisyuk reflection holograms recorded by a high-energy pulsed laser. An intensity threshold must be passed to pattern a multilayer reflection and transmission hologram, which exhibits a nonlinear fringe structure. Numerical evaluations are provided for the laser light intensity, readout diffraction offset angle, transmission of the layer, and thickness of the polymer matrix during hologram recording. A non-sinusoidal surface pattern is formed at the top of the multilayer structure, and its effect on the diffraction properties of the structure becomes significant when the recording tilt angle is increased. Experimental results show that the angle of the diffracted light increases nonlinearly according to the tilt geometry in grating formation. [ABSTRACT FROM AUTHOR]

In CMOS-compatible optical filter designs, SiO2 is often used as the low-index material, limiting the optical contrast (nHi/nLo) to about 2. Using the air as low-index material improves the optical contrast by about 50%, thus increasing the reflectivity and bandwidth at a given design complexity. The design and fabrication of a 4-layered air-dielectric distributed Bragg reflector (DBR) centered at 400 nm using surface micromachining techniques, is presented here. Fabrication is based on the deposition of poly-Si thin films and subsequent thermal oxidation. Selectively removing the Si layers, produces an air/SiO2 filter stack according to the optical design. The width of the air-gaps needed in this application is typically smaller as compared to conventional MEMS devices. The number of layers is also higher, while no electrical contact is required. The concept, the fabrication of 4-layer DBRs and preliminary measurement results are discussed in this paper. [ABSTRACT FROM AUTHOR]

X-ray diffraction from protein crystals includes both sharply peaked Bragg reflections and diffuse intensity between the peaks. The information in Bragg scattering is limited to what is available in the mean electron density. The diffuse scattering arises from correlations in the electron density variations and therefore contains information about collective motions in proteins. Previous studies using molecular-dynamics (MD) simulations to model diffuse scattering have been hindered by insufficient sampling of the conformational ensemble. To overcome this issue, we have performed a 1.1-μs MD simulation of crystalline staphylococcal nuclease, providing 100-fold more sampling than previous studies. This simulation enables reproducible calculations of the diffuse intensity and predicts functionally important motions, including transitions among at least eight metastable states with different active-site geometries. The total diffuse intensity calculated using the MD model is highly correlated with the experimental data. In particular, there is excellent agreement for the isotropic component of the diffuse intensity, and substantial but weaker agreement for the anisotropic component. Decomposition of the MD model into protein and solvent components indicates that protein-solvent interactions contribute substantially to the overall diffuse intensity. We conclude that diffuse scattering can be used to validate predictions from MD simulations and can provide information to improve MD models of protein motions. [ABSTRACT FROM AUTHOR]

3-Pyridyl-5,15-diazaporphyrin nickel(II) serves as a bidentate metalloligand for platinum(II), ruthenium(II), and rhenium(I) metal centers. Single-crystal X-ray diffraction analysis of these metal complexes unambiguously reveals the presence of a dative bond between the outer metal center and the meso-nitrogen atom. The UV/Vis absorption spectra of the complexes show substantially red-shifted bands which are perturbed by outer-metal coordination. This is due to the contribution of metal-to-ligand charge transfer interactions. [ABSTRACT FROM AUTHOR]

A concise and efficient synthesis of (−)-gephyrotoxin from L-pyroglutaminol has been realized. The key step in this approach is a diastereoselective intramolecular enamine/Michael cascade reaction that forms two rings and two stereocenters and generates a stable tricyclic iminium cation. A hydroxy-directed reduction of this intermediate plays a key role in establishing the required cis-decahydroquinoline ring system, enabling the total synthesis of (−)-gephyrotoxin in nine steps and 14 % overall yield. The absolute configuration of the synthetic material was confirmed by single-crystal X-ray diffraction and is consistent with the structure originally proposed for material isolated from the natural source. [ABSTRACT FROM AUTHOR]

X-ray diffraction patterns from still crystals are inherently difficult to process because the crystal orientation is not uniquely determined by measuring the Bragg spot positions. Only one of the three rotational degrees of freedom is directly coupled to spot positions; the other two rotations move Bragg spots in and out of the reflecting condition but do not change the direction of the diffracted rays. This hinders the ability to recover accurate structure factors from experiments that are dependent on single-shot exposures, such as femtosecond diffract-and-destroy protocols at X-ray free-electron lasers (XFELs). Here, additional methods are introduced to optimally model the diffraction. The best orientation is obtained by requiring, for the brightest observed spots, that each reciprocal-lattice point be placed into the exact reflecting condition implied by Bragg's law with a minimal rotation. This approach reduces the experimental uncertainties in noisy XFEL data, improving the crystallographic R factors and sharpening anomalous differences that are near the level of the noise. [ABSTRACT FROM AUTHOR]

Terminally misfolded or unassembled proteins are selectively recognized and cleared by the ER-associated degradation (ERAD) pathway. Suppressor/enhancer of lin-12-like (SEL1L), a component of the dislocation machinery containing the E3 ubiquitin ligase Hrd1, plays an important role in selecting and transporting ERAD substrates for degradation in the endoplasmic reticulum. In this study, the purification, crystallization and preliminary X-ray diffraction analysis of recombinant mouse SEL1L (residues 348-533) are reported. The crystals were obtained by the hanging-drop vapour-diffusion method at pH 8.5 and 277 K using 30% 2-propanol as a precipitant. Optimized crystals diffracted to 3.3 Å resolution at a synchrotron-radiation source. Preliminary X-ray diffraction analysis revealed that the crystals belonged to space group P21 and contained four molecules per asymmetric unit, with a solvent content of 44%. [ABSTRACT FROM AUTHOR]

Hsp90 is a molecular chaperone responsible for the assembly and regulation of many cellular client proteins. In particular, Trap1, a mitochondrial Hsp90 homologue, plays a pivotal role in maintaining mitochondrial integrity, protecting against apoptosis in cancer cells. The N (N-terminal)-M (middle) domain of human Trap1 was crystallized in complex with Hsp90 inhibitors (PU-H71 and BIIB-021) by the hanging-drop vapour-diffusion method at pH 6.5 and 293 K using 15% PEG 8K as a precipitant. Diffraction data were collected from crystals of the Trap1-PU-H71 (2.7 Å) and Trap1-BIIB-021 (3.1 Å) complexes to high resolution at a synchrotron-radiation source. Preliminary X-ray diffraction analysis revealed that both crystals belonged to space group P41212 or P43212, with unit-cell parameters a = b = 69.2, c = 252.5 Å, and contained one molecule per asymmetric unit according to Matthews coefficient calculations. [ABSTRACT FROM AUTHOR]

Low melting point Zr-based filler metals with melting point depressants (MPDs) such as Cu and Ni elements are used for titanium brazing. However, the phase transition of the filler metals in the titanium joint needs to be explained, since the main element of Zr in the filler metals differs from that of the parent titanium alloys. In addition, since the MPDs easily form brittle intermetallics, that deteriorate joint properties, the phase evolution they cause needs to be studied. Zr-based filler metals having Cu content from 0 to 12 at. pct and Ni content from 12 to 24 at. pct with a melting temperature range of 1062 K to 1082 K (789 °C to 809 °C) were wetting-tested on a titanium plate to investigate the phase transformation and evolution at the interface between the titanium plate and the filler metals. In the interface, the alloys system with Zr, ZrNi, and (Ti,Zr)Ni phases was easily changed to a Ti-based alloy system with Ti, TiNi, and (Ti,Zr)Ni phases, by the local melting of parent titanium. The dissolution depths of the parent metal were increased with increasing Ni content in the filler metals because Ni has a faster diffusion rate than Cu. Instead, slow diffusion of Cu into titanium substrate leads to the accumulation of Cu at the molten zone of the interface, which could form undesirable TiCu intermetallics. This study confirmed that Zr-based filler metals are compatible with the parent titanium metal with the minimum content of MPDs. [ABSTRACT FROM AUTHOR]

Knowledge of the macroscopic residual stresses in components of complex high performance alloys is crucial when it comes to considering the safety and manufacturing aspects of components. Diffraction experiments are one of the key methods for studying residual stresses. However a component of the residual strain determined by diffraction experiments, known as microstrain or intergranular residual strain, occurs over the length scale of the grains and thus plays only a minor role for the life time of such components. For the reliable determination of macroscopic strains (with the minimum influence of these intergranular residual strains), the ISO standard recommends the use of particular Bragg reflections. Here we compare the build-up of intergranular strain of two different precipitation hardened IN 718 (INCONEL 718) samples, with identical chemical composition. Since intergranular strains are also affected by temperature, results from room temperature measurement are compared to results at T =550 °C. It turned out that microstructural parameters, such as grain size or type of precipitates, have a larger effect on the intergranular strain evolution than the influence of temperature at the measurement temperature of T =550 °C. The results also show that the choice of Bragg reflections for the diffractometric residual stress analysis is dependent not only on its chemical composition, but also on the microstructure of the sample. In addition diffraction elastic constants (DECs) for all measured Bragg reflections are given. [ABSTRACT FROM AUTHOR]

ABSTRACT The effects of novolac resin (NR) and modified novolac resin (MNR) on the stiffness and toughness of the carbon fiber (CF)/epoxy composites were studied when using these two kinds of modifiers with different physical and chemical performance. The results show that both NR and MNR are excellent toughening agents for the CF/epoxy composites, and the composites treated with MNR present better toughness than that of NR. However, the stiffness of the composites is almost unchanged when adding MNR. The mechanisms were analyzed by fracture studies using scanning electron microscopy and the decrease of cross-link density caused by MNR was deduced to the toughening effects. [ABSTRACT FROM AUTHOR]

ABSTRACT To provide additional functionality to the adhesive polyurethane (PU) matrices, a solution intercalation approach was used to synthesize PU nanocomposite films with layered silicate bentonites modified with different surface ammonium ions. The oxygen permeation through the composite films was correlated to the filler fraction in the composites. The morphology in the composites was characterized using X-ray diffraction and transmission electron microscopy. The nanocomposites were observed to have mixed morphology with varying thicknesses of filler particles. The platelets were also misaligned, and a quantitative value of 50-75% randomness was determined from finite element model predictions. The X-ray diffraction signals also indicated that the basal plane spacing was increased to 3.5 nm in the composites irrespective of the filler type and volume fraction. The oxygen permeation in the case of Tixogel VZ decreased to 25% as compared to pure polymer at 6 wt% (2.13 vol%) filler, and an average aspect ratio of 100 was observed by the finite element permeation models. The Tixogel VP filler, on the other hand, had an excess of modification molecules on the surface and combined with the polarity mismatch (Hansen parameters) of the modification with the PU chains led to an increase in the oxygen permeation through the nanocomposite films. [ABSTRACT FROM AUTHOR]

Symmetric Bragg-case reflections from a thick, ideally imperfect, crystal slab are studied mostly by analytical means. The scattering transfer function of a thin mosaic layer is derived and brought into a form that allows for analytical approximations or easy quadrature. The Darwin-Hamilton equations are generalized, lifting the restriction of wavevectors to a two-dimensional scattering plane. A multireflection expansion shows that wavevector diffusion can be studied independently of the real-space coordinate. Combining analytical arguments and Monte Carlo simulations, multiple Bragg reflections are found to result in a minor correction of the reflected intensity, a moderate broadening of the reflected azimuth angle distribution, a considerable modification of the polar angle distribution, and a noticeable shift and distortion of rocking curves. [ABSTRACT FROM AUTHOR]

Purpose The biological optimization of proton therapy can be achieved only through a detailed evaluation of relative biological effectiveness (RBE) variations along the full range of the Bragg curve. The clinically used RBE value of 1.1 represents a broad average, which disregards the steep rise of linear energy transfer (LET) at the distal end of the spread-out Bragg peak (SOBP). With particular attention to the key endpoint of cell survival, our work presents a comparative investigation of cell killing RBE variations along monoenergetic (pristine) and modulated (SOBP) beams using human normal and radioresistant cells with the aim to investigate the RBE dependence on LET and intrinsic radiosensitvity. Methods and Materials Human fibroblasts (AG01522) and glioma (U87) cells were irradiated at 6 depth positions along pristine and modulated 62-MeV proton beams at the INFN-LNS (Catania, Italy). Cell killing RBE variations were measured using standard clonogenic assays and were further validated using Monte Carlo simulations and the local effect model (LEM). Results We observed significant cell killing RBE variations along the proton beam path, particularly in the distal region showing strong dose dependence. Experimental RBE values were in excellent agreement with the LEM predicted values, indicating dose-averaged LET as a suitable predictor of proton biological effectiveness. Data were also used to validate a parameterized RBE model. Conclusions The predicted biological dose delivered to a tumor region, based on the variable RBE inferred from the data, varies significantly with respect to the clinically used constant RBE of 1.1. The significant RBE increase at the distal end suggests also a potential to enhance optimization of treatment modalities such as LET painting of hypoxic tumors. The study highlights the limitation of adoption of a constant RBE for proton therapy and suggests approaches for fast implementation of RBE models in treatment planning. [ABSTRACT FROM AUTHOR]

(LiAg)TaO (0 ≤ x ≤ 0.15) ceramics were fabricated by a mixed-oxide solid-state sintering route. Compositions with x ≤ 0.1 sintered into single-phase compounds and could be indexed according to the rhombohedral, $$ R{\bar{3}}c $$ or R3 c structure. For x > 0.1, x-ray diffraction revealed second-phase formation, probably LiTaO and AgTaO. It was noticed that the metastable and stable phase solubility limits for Li in AgTaO were x < 0.05 and 0.10 < x < 0.15, respectively. Raman and dielectric measurements confirmed the existence of a ferroelectric state in the compositions with x ≥ 0.05. This triggering of ferroelectricity supports the premise that substitution of relatively smaller ions increases the displacement of the A-site cation. The transition temperature was found to increase as a function of increasing Li concentration. Low-temperature (<100 K) Raman spectra and electron diffraction indicated that Li-doped AgTaO ceramics seem to adopt new tilt systems. [ABSTRACT FROM AUTHOR]

Nanocrystalline Gd-doped GdAlSiO mullite powders with x from 0.005 to 0.025 have been synthesized via a facile coprecipitation technique. X-ray diffraction results revealed that o-mullite was detected as the major phase for x = 0.0 to 0.01, whereas corundum α-AlO was predominant for x = 0.025. It was found that the volume of the mullite unit cell increased with Gd ion incorporation. Differential scanning calorimetry thermograms evinced that the exothermic peak temperature of mullite shifted to lower values with Gd ion insertion. Transmission electron microscopy observations of pure mullite nanoparticles displayed orthorhombic-like shapes. Meanwhile, at 0.5% Gd ion content, the mullite particles exhibited platelet-like shapes, which distorted into spheroidal-like crystals at high Gd ion contents (1% and 2.5%). The photoluminescence spectra indicated that the intensity of the emission spectra improved considerably with Gd ion doping. On the other hand, dielectric measurements of sintered samples showed that the maximum dielectric loss values were 1.7 and 1.4 at 1.5 MHz and 1.5 GHz, respectively, with 2.5% Gd ion content. [ABSTRACT FROM AUTHOR]

Nanocrystalline ZnSe films were prepared by the chemical bath deposition technique by varying the pH of the reaction bath from 9.2 to 10.6, and the physical properties of the annealed films were investigated. The x-ray diffraction profiles of the samples showed hexagonal structure of ZnSe nanocrystallites except for films deposited at pH 10.6. Strain was compressive, but became tensile with increase in pH. Topographical studies by atomic force microscopy showed a smooth surface of the samples deposited at higher pH and therefore low surface roughness. Optical studies revealed homogeneous grain shape and size. The thickness, grain size, and bandgap of the samples showed consistent results. The photoluminescence emission peaks occurred at the same wavelength for different pH values. The physical properties of the annealed samples seem to make them suitable for application as buffer layers in thin-film solar cells. [ABSTRACT FROM AUTHOR]

(Cu1-xAgx)2O oxide films with cuprite structure are presented. The p-type film demonstrates an exceptional increase in hole cconcentration up to 1.18×1021 cm-3 with increasing Ag to 33 at.%. It is revealed from high-resolution transmission electron microscopy along with X-ray diffraction analysis that the oxide remains a single phase with the Ag content up to 33 at.%. Raman spectroscopy measurements exhibit different symmetrical features for the oxide than those of Cu2O. This suggests that the valence-band edge level can be raised as a result of the incorporation of Ag1+ into Cu2O, which is verified by the small acceptor ionization energy observed for the (Cu0.67Ag0.33)2O. In addition, the coexistence of Cu1+ and Ag1+ is shown to suppress variable-range-hopping conduction, demonstrating weakly degenerate semiconductor behavior. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we present a novel method of gas leakage detection based on self-mixing interference with an extremely compact Er3+–Yb3+ codoped Distributed Bragg Reflector (EYDBR) fiber laser. According to the simulation and theoretical analysis of gas leakage of tank, we infer that the vibration frequency peak of tank caused by gas leakage increases with the internal pressure. In the experiment, the results agree with the theoretical prediction and the relevance of polynomial fitting about the spectrum peak of tank vibration and internal pressure is 0.99725. Thus, we can get the internal pressure of tank by measuring the vibration frequency peak of tank. Moreover, it has important significance in the prevention of the accident of flammable or explosive gas leakage. [Copyright &y& Elsevier]

Diffraction of light by ultrasound is theoretically investigated with the help of the 2D equation of coupled modes. A 2D theory rigorously describing the diffraction at arbitrary, including large, angles is developed. The 2D equation of coupled modes is derived for optically isotropic and optically anisotropic media. The equation is solved in the practically important case of the Bragg diffraction. Distinctions between the 2D and 1D descriptions of the diffraction are discussed. [ABSTRACT FROM AUTHOR]

We report the condensation of microcavity exciton-polaritons at Γ points located on the boundary between the third and higher Brillouin zones in hexagonal lattices: triangular and honeycomb geometries. We collect experimental evidence that supports the finite momentum condensation: (1) the coherent Bragg peaks formed at nonzero Γ points; (2) the nonlinear intensity increase in the exciton-polariton emission at quantum degeneracy threshold; (3) the spectral linewidth behavior: narrowing near threshold and broadening above threshold; and (4) the equivalent 4fy3-3x2y-like orbital symmetry in real space. The f-orbital state at Γ points appears as a metastable momentum valley to trap exciton-polaritons, which is explained by single-particle band-structure calculations. [ABSTRACT FROM AUTHOR]

The ability to confine photoactive catalysts within metal organic framework (MOF) materials affords the opportunity to expand the functional diversity of these materials into solar-based applications. Here, two new Ru(ll) tris(2,2'-bipyridine) (RuBpy)-based photoactive materials derived from reactions between Zn(ll) ions and l,3,5-tris(4-carboxyphenyl)benzene and templated by the presence of RuBpy (RWLC-1 and RWLC-2) are described with regard to structure and RuBpy photophysics. RuBpy cations have been successfully encapsulated within the cavities (RWLC-1 ) and channels (RWLC-2) of the new negatively charged frameworks, both of which are synthesized simultaneously in a single reaction vial. Single-crystal X-ray diffraction studies allowed for determination of the RuBpy position within crystal voids. RuBpy encapsulated in each of the two new MOFs exhibits biphasic triplet metal to ligand charge transfer (³MLCT) emission decay lifetimes (τRWLC-1-faSt = 237 ns, τRWLC-1-slow = 1.60 µs, τRWLC-2-fast = 171 ns, and τRWLC.2-slow = 797 ns at 25 °C) consistent with two populations of RuBpy complexes, one being encapsulated in highly space-restricted cavities giving rise to a longer 3MLCT lifetime, while the second is encapsulation within a larger nonperiodic pore or defect with a coencapsulated quencher giving rise to short emission lifetimes. Taken together, these results represent examples of the templating ability of RuBpy to produce novel materials with distinct photophysical environments of the encapsulated guests. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the nonBragg bandgap (NBBG) resulting from interference between two transverse guided wave modes in an axisymmetric duct with periodic walls. We find that the NBBG bandwidth is proportional to both the height and shape factor of the wall undulations. The shape factor is defined as the norm of the major Fourier component of the periodic wall profile. Varying the height directly tunes the bandwidth, while manipulating the wall profile results in a slight change in the shape factor, which leads to fine-tuning of the bandgap. We also find that for a fixed height, the NBBG width is related to the area under the curve for the product of the wall profile and a half-period sine or cosine function. We propose an area estimation method according to which a larger area results in a wider NBBG. A numerical example reveals that NBBG fine-tuning can be achieved by carefully varying the shape factor. The results will benefit the design of band structures, especially subtle modifications by selecting suitable wall undulations. [Copyright &y& Elsevier]

The giant amplification and lasing of terahertz radiation due to stimulated generation of plasmons in graphene with a distributed planar Bragg resonator strongly coupled to THz radiation are predicted. The amplification of terahertz waves at the plasmon resonance frequencies is several orders of magnitude stronger than it is away from the resonances. The lasing at the plasmon resonance is achieved when the net plasmon gain in graphene approaches the negative of the radiative damping of the resonant plasmons, which ensures high plasmon coherence and self-excitation of a collective plasmon mode. It is shown that the dynamic and frequency ranges as well as the energy conversion efficiency of the terahertz graphene amplifier can be strongly enhanced in the structure with a narrow-slit Bragg grating and/or thin barrier layer. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes high efficiency 1D silicon–silicon carbide (Si–SiC) and silicon–silicon monoxide (Si–SiO) grating structures which can be used as optical interconnects in optical communication system. Here absorption, transmission and diffraction losses are considered to optimize the grating structure. The simulation results show that the reflectance is zero at the wavelength of 1μm for silicon–silicon carbide and 1.25μm for silicon–silicon monoxide grating structure. It is seen that the diffraction efficiency is nearly constant that is more than 99.19% in case of Si–SiC and 99.5% in case of Si–SiO grating structure with respect to detuning from Bragg's angle of incidence, which varies from −1 radian to +1 radian. This simulation is done by using plane wave expansion method. [Copyright &y& Elsevier]

In this paper we describe elements of photonic crystal surface-emitting laser (PCSEL) design and operation, highlighting that epitaxial regrowth may provide advantages over current designs incorporating voids. High coupling coefficients are shown to be possible for all-semiconductor structures. We introduce type I and type II photonic crystals (PCs), and discuss the possible advantages of using each. We discussed band structure and coupling coefficients as a function of atom volume for a circular atom on a square lattice. Additionally we explore the effect PC atom size has on in-plane and out-of-plane coupling. We conclude by discussing designs for a PCSEL combined with a distributed Bragg reflector to maximize external efficiency. [ABSTRACT FROM AUTHOR]

Since the introduction of locally resonant (LR) phononic meta-materials and structures a decade ago, there has been a quest for wide band-gaps of elastic wave attenuation in a low frequency range of practical importance. We investigate periodic Euler-Bernoulli beams suspended with two degrees of freedom force-moment resonators. Based on mathematical analysis and calculations, we present their dispersive characteristics in flexural wave attenuation and propagation. As a prime focus, we identify the appearance a below-resonance band-gap of Bragg-scattering (BS) type--in addition to the normal post-resonance BS band-gap--and the dependence of their edge frequencies on the resonator parameters. Furthermore, we present a full characterization of four different groups of pass and stop frequency bands and six distinct types of transitions between them, with conditions for all band edge frequencies. Our results indicate potentially richer dispersion properties in LR periodic structures with resonators of multiple degrees of freedom than those with the conventional force-only (or moment-only) resonators. [ABSTRACT FROM AUTHOR]

A 13.5-pair Al0.98In0.02N/Al0.77Ga0.23N distributed Bragg reflector (DBR) was grown by molecular beam epitaxy on an AlN template substrate. The DBR exhibited a peak reflectivity of 83.9% at 246 nm within the deep solar-blind ultraviolet region and a stopband width of 18 nm. The average refractive index contrast for the DBR was 9.25% at 246 nm, which is relatively high compared with that of a traditional Al(Ga)N/(Al)GaN DBR. Simulated results indicated that a 25.5-pair Al0.98In0.02N/Al0.77Ga0.23N DBR will provide a reflectivity higher than 99% and a 19 nm wide stopband with a center wavelength of 246 nm. [ABSTRACT FROM AUTHOR]

We report an electrically tunable reflective color display based on a colloidal photonic crystal. The device exhibits a low driving voltage and reasonably fast response time. 3D finite difference time domain (FDTD) method and Bragg formula are used for theoretical investigation and interpretation of the experimental data. Disorder effect and its influences on display performance are analyzed. Other interesting applications discussed include fashion decoration, counterfeit waterproof, and chameleon skin. [ABSTRACT FROM AUTHOR]

A set of four confocal laser beams of 1064-nm wavelength is used to prepare optically induced crystals of submicron particles in aqueous solution. Thousands of polystyrene spheres of about 200 nm in diameter are trapped in three dimensions. Bragg scattering patterns obtained with a probe beam of 532-nm wavelength are in agreement with the calculated lattice structure and its polarization dependence. The decay and rise of the Bragg scattering intensity upon switching the lattice off and on reveal the Brownian motion dynamics of the particles in the periodic optical trapping potential. Experimental results agree well with results from trajectory simulations based on the Langevin equation. The results exhibit the interplay between Brownian motion and deterministic forces in an inhomogeneous (near-)periodic optical trapping potential. [ABSTRACT FROM AUTHOR]

The synthesis of quasicrystals and observation of their unexpected 10-fold symmetric diffraction pattern by D. Shechtman and co-workers 1982-1984 provide a natural bridge for bringing solid state (condensed matter) physics within the purview of Santilli's 1967-2006 Lie-admissible generalization of quantum mechanics (QM) under the name "hadronic" mechanics (HM) via our recent non-unitary scattering theory of HM for deep-inelastic e^--p and e^+-e^- scattering processes. This is achieved in this paper by a re-formulation and elaboration of Bragg's law of diffraction for quasicrystals under the title Geno-Bragg's law which permits identification of the deformed quasicrystalline state with 10^*x10 representation of SU(3) symmetry. Essentially, because only 1-,2-,3-,4- and 6-fold but not 5-fold point symmetry of perfectly periodic crystal lattice are allowed in 3-dimensional (3D) real or reciprocal lattice space, a (non-unitary) deformation of the allowed (cubic) 4-fold and (hexagonal) 6-fold symmetry axes into a common diffraction (square-hexagon) geno-plane having 10-fold point symmetry is achievable as envisaged in HM. As a result, the current icosahedron approximant structure is replaced by cube-hexagon genospace structure that permits determination of atomic distribution in quasicrystals as holographic (periodic) structure. Further elaboration of Geno-Bragg's law to high energy (relativistic) deep-inelastic scattering processes described by current-current interaction models of neutron synthesis/decay is applied to the determination of the structure of the neutron and the implications for geno-renormalization of mass and the ratios of the masses of the elementary particles are discussed. [ABSTRACT FROM AUTHOR]

We report the structural and magnetic properties of rare-earth substituted spin-chain compounds Ca2.75R0.25Co2O6 (R = Dy and Lu). The Rietveld refinement of neutron and x-ray powder diffraction patterns confirms the single-phase formation of both compounds in the rhombohedral structure (space group R3̅c). The derived values (from the analysis of the neutron diffraction patterns at 50 K) of the bond-valence sum indicate a reduction in the oxidation state of the cobalt ions at the trigonal prism (TP) site (6a) with R substitution, which is further supported by low temperature neutron diffraction [where a zero value of the ordered moment at the 6b site and a reduction in the values of the maximum ordered moment at the TP site have been observed] and dc magnetization studies. In the neutron diffraction patterns, additional Bragg peaks appear for both compounds below Néel temperature (TN) of ~16 K, indicating the onset of an antiferromagnetic ordering of cobalt spin chains on the triangular lattice. The magnetic structure corresponds to a spin density wave (SDW) structure [with a propagation vector k={0,0,1.02}], having c axis as a direction of both moment and modulation. For both compounds, the refined values of the ordered moment at the 18e, 6b, and 6a sites are ~0.03(2),0.02(2), and 4.2 (2) μB, respectively. Unlike the parent compound Ca3Co2O6, no temperature dependence as well as no time dependence in the intensity of the strongest antiferromagnetic reflection (10 τ), corresponding to the propagation vector k = {0, 0, 1.02}, has been observed down to 1.5 K confirming that the SDW structure is stabilized by the substitution with rare-earth ions. The stabilization of the SDW structure and the observed decrease in the values of TN could be due to a decrease in the value of positive FM intrachain exchange interaction J with the rare-earth substitution in a system with competing intrachain and interchain exchange interactions. [ABSTRACT FROM AUTHOR]

The features of the propagation of a neutron through a crystal at nearly Bragg energies has been studied within the framework of the preparation of an experiment on the search for the electric dipole moment of a neutron by the crystal diffraction method. The time of passage of the neutron through the crystal has been studied as a function of the deviation from the Bragg condition. The anomalous behavior of the dispersion of the neutron, i.e., the energy dependence of its average velocity, has been observed. It has been shown that the derivative dv/dE for the diffracting neutron at nearly Bragg energies can be three or four orders of magnitude larger than this derivative for a free neutron. This opens new possibilities in precision neutron spectroscopy. [ABSTRACT FROM AUTHOR]

We trace the historical development of W. L. Bragg's `law' and the key experimental observation which made it possible using polychromatic radiation at a time when neither X-ray wavelengths nor cell constants were known. This led, through his phasing and solving large mineral structures (without use of a computer), to work on metals, proteins, bubble rafts and his X-ray microscope. The relationship of this to early X-ray microdiffraction is outlined, followed by a brief review of electron microdiffraction methods, where electron-probe sizes smaller than one unit cell can be formed with an interesting `failure' of Bragg's law. We end with a review of recent femtosecond X-ray `snapshot' diffraction from protein nanocrystals, using an X-ray laser which generates pulses so short that they terminate before radiation damage can commence, yet subsequently destroy the sample. In this way, using short pulses instead of freezing, the nexus between dose, resolution and crystal size has been broken, opening the way to time-resolved diffraction without damage for a stream of identical particles. [ABSTRACT FROM AUTHOR]