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The effect of annealing current density on the structure of the resulting nanocrystalline phase in the amorphous [Fe.sub.73.9][Nb.sub.3.1][Cu.sub.0.9][Si.sub.13.2][B.sub.8.9] alloy is examined. The ex situ Mossbauer spectroscopy measurements on current annealed samples have indicated a variation, with increasing current density, in the composition of the nanocrystalline grains and/or the amorphous grain boundary phase.

M3 reflection intensity ([I.sub.M3]) from tetanized, intact skeletal muscle fiber bundles was measured during sinusoidal length oscillations at 2.8 kHz, a frequency at which the myosin motor's power stroke is greatly reduced. [I.sub.M3] signals were approximately sinusoidal, but showed a 'double peak' distortion previously observed only at lower oscillation frequencies. A tilting lever arm model simulated this distortion, where [I.sub.M3] was calculated from the molecular structure of myosin subfragment 1 (S1). Simulations showed an isometric lever arm disposition close to normal to the filament axis at isometric tension, similar to that found using lower oscillation frequencies, where the power stroke contributes more toward total S1 movement. Inclusion of a second detached S1 in each actin-bound myosin dimer increased simulated [I.sub.M3] signal amplitude and improved agreement with the experimental data. The best agreement was obtained when detached heads have a fixed orientation, insensitive to length changes, and similar to that of attached heads at tetanus plateau. This configuration also accounts for the variations in relative intensity of the two main peaks of the M3 reflection substructure after a length change. This evidence of an [I.sub.M3] signal distortion when power stroke tilting is suppressed, provided that a large enough amplitude of length oscillation is used, is consistent with the tilting lever arm model of the power stroke. skeletal muscle; X-ray diffraction; muscle mechanics; molecular motors; subfragment 1 structure

The liquid crystalline phase structures and the time-dependent dynamics of ternary systems made up Brij-35, dibutyl ether and 10 mM Na/K buffer have been investigated. A series of phase diagrams at 10, 20, 30, 40 and 60 degrees C have been derived using small and wide-angle x-ray scattering. These liquid crystals have distinct, nanoscaled hydrophobic and hydrophilic domains separated by a surfactant interface. Results show Brij-35 exists as a crystalline lamellar Lc phase with a repeat distance of 170 angstroms. Lammllar, cubic, micellar and isotropic surfactant liquid structure were observed in the oil-poor part of the phase diagrams.

The human telomeric G-quadruplex structural motif of DNA has come to be known as a new and stimulating target for anticancer drug discovery. Small molecules that interact with G-quadruplex structures in a selective way have gained impressive interest in recent years as they may serve as potential therapeutic agents. Here, we show how circular dichroism, UV resonance Raman and small angle X-ray scattering spectroscopies can be effectively combined to provide insights into structural and molecular aspects of the interaction between human telomeric quadruplexes and ligands. This study focuses on the ability of berberine and palmatine to bind with human telomeric quadruplexes and provides analysis of the conformational landscape visited by the relevant complexes upon thermal unfolding. With increasing temperature, both free and bound G-quadruplexes undergo melting through a multi-state process, populating different intermediate states. Despite the structural similarity of the two ligands, valuable distinctive features characterising their interaction with the G-quadruplex emerged from our multi-technique approach. [ABSTRACT FROM AUTHOR]

Photoresponsive materials feature properties that can be adjusted by light near-instantaneously, reversibly, and with high spatiotemporal precision. There is considerable interest in maximising the degree of photoswitching, and in measuring this degree during illumination in complex environments. We study the switching of photoresponsive lipid membranes that allow for precise and reversible manipulation of membrane shape, permeability, and fluidity. Though these macroscopic responses are clear, it is unclear how large the changes of trans/cis ratio are, and whether they can be improved. Here, we used small-angle X-ray scattering to measure the thickness of photoswitchable lipid membranes, and we correlate lipid bilayer thickness to trans/cis ratios. This reveals an unexpected dependency of photoswitching ratio upon aqueous phase composition. In buffer with ionic strength, we observe thickness variations twice as large as previously observed. Furthermore, soft X-rays can quantitatively isomerise photolipid membranes to the all-trans state; enabling X-ray-based membrane control. High energy X-rays do not influence the state of the photoswitches, presumably because they deposit less dose in the sample.

Functional coatings based on self-assembled lyotropic liquid crystals have the potential for applications such as biosensing, drug delivery and nanotemplating. Here we demonstrate the design and in-depth characterization of glycerol monooleate based liquid crystalline coatings on silicon wafers using drop casting and spin coating techniques. In situ time-resolved grazing incidence small angle X-ray scattering (GISAXS) measurements were used to monitor the coating formation and its response to increasing relative humidity conditions between 5 and 100%. Additional atomic force microscopy (AFM) measurements were applied to visualize the coating nanostructure. Structural transformations through ordered intermediate phases to the sponge- and lamellar phase were observed during ethanol evaporation. Relative humidity dependent GISAXS results revealed gradual phase transitions from the lamellar via the gyroid type cubic phase to the diamond type bicontinuous cubic structure between 5 and 100% relative humidity. The detailed insights into the formation and transformation of the coating nanostructures in this system may provide essential knowledge for the comprehensive design of functional nanostructured surfaces in biomedical applications. [ABSTRACT FROM AUTHOR]

Specimens of the amorphous Fe[sub 72]Cu[sub 1]Nb[sub 4.5]Si[sub 13.5]B[sub 9] alloy have been nanocrystallized by furnace (FA) and current (CA) annealing and analyzed by simultaneous small-angle (SAXS) and wide-angle (WAXS) x-ray scattering using the beam-line 5.2L at Elettra Synchrotron Source, Trieste. The analysis has been carried out also dynamically on untreated samples current heated in situ. Significant differences in the SAXS regime have been observed between the FA and CA samples having the same amount of nanocrystallization as determined from previous WAXS and Mo¨ssbauer measurements. These differences can be attributed to a lower contrast of the nanocrystallites in the CA samples as compared to FA samples. The Mo¨ssbauer spectra show that in FA and CA samples the nanocrystalline grains consist of a nonstoichiometric partially disordered Fe[sub 3]Si phase, and indicate the presence of boron atoms in the nanocrystals of CA samples. This is in agreement with the lower contrast found by SAXS and implies a lower segregation of boron atoms and/or of borides at the boundaries of nanocrystallites of CA samples, accounting for their lower brittleness. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Lead halide perovskites have attracted tremendous attention in photovoltaics due to their impressive optoelectronic properties. However, the poor stability of perovskite-based devices remains a bottleneck for further commercial development. Two-dimensional perovskites have great potential in optoelectronic devices, as they are much more stable than their three-dimensional counterparts and rapidly catching up in performance. Herein, we demonstrate high-quality two-dimensional novel perovskite thin films with alternating cations in the interlayer space. This innovative perovskite provides highly stable semiconductor thin films for efficient near-infrared light-emitting diodes (LEDs). Highly efficient LEDs with tunable emission wavelengths from 680 to 770 nm along with excellent operational stability are demonstrated by varying the thickness of the interlayer spacer cation. Furthermore, the best-performing device exhibits an external quantum efficiency of 3.4% at a high current density (J) of 249 mA/cm2 and remains above 2.5% for a J up to 720 mA cm−2, leading to a high radiance of 77.5 W/Sr m2 when driven at 6 V. The same device also shows impressive operational stability, retaining almost 80% of its initial performance after operating at 20 mA/cm2 for 350 min. This work provides fundamental evidence that this novel alternating interlayer cation 2D perovskite can be a promising and stable photonic emitter.

Lipid exchange among citrem nanoparticles and an ethanol micellar solution containing soy phosphatidylcholine was investigated in situ by coupling small angle X-ray scattering with a microfluidic device. The produced soy phosphatidylcholine/citrem nanoparticles have great potential in the development of hemocompatible nanocarriers for drug delivery. [ABSTRACT FROM AUTHOR]

A new carbon model derived from in situ small-angle X-ray scattering (SAXS) enables a quantitative description of the voltage-dependent arrangement and transport of ions within the nanopores of carbon-based electric double-layer capacitors. In the first step, ex situ SAXS data for nanoporous carbon-based electrodes are used to generate a three-dimensional real-space model of the nanopore structure using the concept of Gaussian random fields. This pore model is used to derive important pore size characteristics, which are cross-validated against the corresponding values from gas sorption analysis. In the second step, simulated in situ SAXS patterns are generated after filling the model pore structure with an aqueous electrolyte and rearranging the ions via a Monte Carlo simulation for different applied electrical potentials. These simulated SAXS patterns are compared with in situ SAXS patterns recorded during voltage cycling. Experiments with different cyclic voltammetry scan rates revealed a systematic time lag between ion transport processes and the applied voltage signal. Global transport into and out of nanopores was found to be faster than the accommodation of the local equilibrium arrangement in favor of sites with a high degree of confinement. [ABSTRACT FROM AUTHOR]

Coarse grained, well crystalline γ-LiAlO2 (P43212) is known as an electronic insulator and a very poor ion conductor with the lithium ions occupying tetrahedral voids in the oxide structure. The introduction of structural disorder such as point defects or higher-dimensional defects, however, may greatly affect ionic conduction on both short-range as well as long-range length scales. In the present study, we used high-energy ball milling to prepare defect-rich, nanocrystalline LiAlO2 that was characterized from a structural point of view by powder X-ray diffraction, TEM as well as small angle X-ray scattering (SAXS). Temperature-dependent conductivity spectroscopy revealed an increase of the room-temperature ionic conduction by several orders of magnitude when going from microcrystalline γ-LiAlO2 to its nanocrystalline form. The enhanced ion transport found is ascribed to the increase of Li ions near defective sites both in the bulk as well as in the large volume fraction of interfacial regions in nano-LiAlO2. The nanocrystalline ceramic prepared at long milling times is a mixture of γ-LiAlO2 and the high-pressure phase δ-LiAlO2; it adapts an amorphous like structure after it has been treated in a planetary mill under extremely harsh conditions. [ABSTRACT FROM AUTHOR]

The loss in performance during fuel cell operation is one of the critical factors that hamper fuel cells commercialization. This paper presents a research activity related to high temperature polymer electrode membrane fuel cell (HT-PEMFC) degradation. The aim of the study is to investigate catalyst degradation of membrane electrode assemblies (MEAs) subjected to load cycles. Two HT-PEM MEAs have been subjected to accelerated ageing tests based on load cycling. The cycles profile has been chosen in order to enhance catalyst degradation. Both the tests show a fuel cell performance loss lower than 30mV after 100,000 cycles at 600 mA cm-2. In order to analyze the catalyst evolution, synchrotron small angle X-ray scattering (SAXS) has been employed. The catalyst degradation of the two conditioned samples has been compared with the data obtained from a new MEA that has been used as reference sample. The SAXS results showed a mean size increase of the platinum nanoparticles up to the 100%. [ABSTRACT FROM AUTHOR]