Small-angle Data Research Articles

Disk-integrated and disk-resolved photometry of the Moon with GaoFen-4 space observations

The GaoFen-4 (GF-4) satellite obtained high-resolution images of the entire lunar disk in a single exposure without atmospheric disturbance. These data are favorable for the study of both disk-resolved and disk-integrated photometric properties of the Moon. Using the GF-4 observations, we modeled the lunar reflectance phase functions with the Hapke model and analyzed the lunar photometric properties. The results indicate that the lunar surface exhibits pronounced backscattering, and the maria appear to be smoother compared to the highlands. The disk-resolved and disk-integrated models produced different best-fit parameters for the whole Moon, with the disk-integrated model fitting the small phase angle data better, and the disk-resolved model showing a more favorable appearance at large phase angles. By calculating the disk-integrated phase function with a disk-resolved method, the study confirms the equivalence of the two models, albeit with a small discrepancy due to an imperfect approximation of the roughness function. This discrepancy is due to the different forms of the phase function used in the models. The geometric albedo of the Moon derived from the disk-resolved model is 0.137 and the spherical albedo is 0.063 for Band 3 of GF-4 at 560.6 nm. This study observed an arched phase curve of the ratio of reflectance in two wavelengths, indicating a phenomenon of phase reddening at small phase angles and bluing at large phase angles.

X‐ray Solution Scattering Studies at the Life Sciences X‐ray Scattering (LiX) Beamline

Solution small angle X-ray scattering (SAXS) is a method to characterize the behavior of particles such as proteins and protein complexes in solution. Information about particle size and shape as well as oligomeric state can be determined from the 1D scattering profiles. The life sciences X-ray scattering (LiX) beamline at NSLSII operates in two modes: I) X-ray imaging and II) solution scattering (BioSAXS). Here, we discuss the types of BioSAXS measurements performed, automation, remote collection, data processing and examples of user data. Static SAXS measurements are high throughput and managed with a sample handler, with room for up to 360 samples organized into 18-well holders. Each holder contains two rows that are connected to separate channels of a flow cell that aligns with the X-ray beam. As the sample flows into the channel and is illuminated by the X-ray beam, small angle (SAXS) and wide angle (WAXS) data is collected simultaneously on two detectors with a q-range of 0.006Å-1 to 3.2 Å-1. This type of measurement requires pure, monodisperse sample and for the case when mixed populations exist, such as dimers and monomers, static SAXS will produce poor data quality. Therefore, size exclusion chromatography coupled with SAXS (SEC-SAXS) should be considered to separate each species. At LiX, the center flow channel is connected to an HPLC system, which allows for seamless integration of SEC-SAXS into the workflow without having to make changes to the beamline hardware setup. Once data is collected, it is packaged into HDF5 format and automatically processed. Data is transferred to users via Globus. We now offer remote collection and users can ship samples in holders or 96-well plates. Samples sent in plates are loaded into an Opentrons liquid handling system and transferred into sample holders. Additionally, having the Opentrons allow us to manipulate sample conditions through dilution, mixing and/or screening right before measurement.

Multilayer Mg/NbO thin film nanostructures

Multilayer (Mg/NbOx)82 nanostructures with different thickness of Mg layers and the constant thickness of NbOx layers have been prepared. The samples were obtained by ion-beam sputtering of metal and ceramic target and multiple consecutive depositions of NbOx and Mg layers onto substrates. The multilayering of the samples was confirmed by X-ray small-angle reflectometry. The thickness of one bilayer (magnesium layer + niobium oxide layer) was determined based on the small-angle data. The thickness of one bilayer in the studied structures was varied from 2.2 nm to 6.2 nm. Despite the separated deposition the magnesium layer's surface in the (Mg/NbOx)82 nanostructures was partially oxidized. The electric percolation transition was observed in the (Mg/NbOx)82 nanostructures at increase of the Mg layers thickness. At small bilayer thicknesses (less than 4.5 nm) the Mg phase is the partially oxidized nanogranules and the charge transfer in such samples is carried out by electron tunneling between the nanogranules. At larger bilayer thickness, the multilayer samples exhibit usual metallic conductivity.

Carbonaceous Materials Investigated by Small-Angle X-ray and Neutron Scattering

Carbonaceous nanomaterials have become important materials with widespread applications in battery systems and supercapacitors. The application of these materials requires precise knowledge of their nanostructure. In particular, the porosity of the materials together with the shape of the pores and the total internal surface must be known accurately. Small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) present the methods of choice for this purpose. Here we review our recent investigations using SAXS and SANS. We first describe the theoretical basis of the analysis of carbonaceous material by small-angle scattering. The evaluation of the small-angle data relies on the powerful concept of the chord length distribution (CLD) which we explain in detail. As an example of such an evaluation, we use recent analysis by SAXS of carbide-derived carbons. Moreover, we present our SAXS analysis on commercially produced activated carbons (ACN, RP-20) and provide a comparison with small-angle neutron scattering data. This comparison demonstrates the wealth of additional information that would not be obtained by the application of either method alone. SANS allows us to change the contrast, and we summarize the main results using different contrast matching agents. The pores of the carbon nanomaterials can be filled gradually by deuterated p-xylene, which leads to a precise analysis of the pore size distribution. The X-ray scattering length density of carbon can be matched by the scattering length density of sulfur, which allows us to see the gradual filling of the nanopores by sulfur in a melt-impregnation procedure. This process is important for the application of carbonaceous materials as cathodes in lithium/sulfur batteries. All studies summarized in this review underscore the great power and precision with which carbon nanomaterials can be analyzed by SAXS and SANS.

What Can We Learn from Wide-Angle Solution Scattering?

Extending collection of x-ray solution scattering data into the wide-angle regime (WAXS) can provide information not readily extracted from small angle (SAXS) data. It is possible to accurately predict WAXS scattering on the basis of atomic coordinate sets and thus use it as a means of testing molecular models constructed on the basis of crystallography, molecular dynamics (MD), cryo-electron microscopy or ab initio modeling. WAXS data may provide insights into the secondary, tertiary and quaternary structural organization of macromolecules. It can provide information on protein folding and unfolding beyond that attainable from SAXS data. It is particularly sensitive to structural fluctuations in macromolecules and can be used to generate information about the conformational make up of ensembles of structures co-existing in solution. Novel approaches to modeling of structural fluctuations can provide information on the spatial extent of large-scale structural fluctuations that are difficult to obtain by other means. Direct comparison with the results of MD simulations are becoming possible. Because it is particularly sensitive to small changes in structure and flexibility it provides unique capabilities for the screening of ligand libraries for detection of functional interactions. WAXS thereby provides an important extension of SAXS that can generate structural and dynamic information complementary to that obtainable by other biophysical techniques.

Ultrafast anisotropic protein quake propagation after CO photodissociation in myoglobin

"Protein quake" denotes the dissipation of excess energy across a protein, in response to a local perturbation such as the breaking of a chemical bond or the absorption of a photon. Femtosecond time-resolved small- and wide-angle X-ray scattering (TR-SWAXS) is capable of tracking such ultrafast protein dynamics. However, because the structural interpretation of the experiments is complicated, a molecular picture of protein quakes has remained elusive. In addition, new questions arose from recent TR-SWAXS data that were interpreted as underdamped oscillations of an entire protein, thus challenging the long-standing concept of overdamped global protein dynamics. Based on molecular-dynamics simulations, we present a detailed molecular movie of the protein quake after carbon monoxide (CO) photodissociation in myoglobin. The simulations suggest that the protein quake is characterized by a single pressure peak that propagates anisotropically within 500 fs across the protein and further into the solvent. By computing TR-SWAXS patterns from the simulations, we could interpret features in the reciprocal-space SWAXS signals as specific real-space dynamics, such as CO displacement and pressure wave propagation. Remarkably, we found that the small-angle data primarily detect modulations of the solvent density but not oscillations of the bare protein, thereby reconciling recent TR-SWAXS experiments with the notion of overdamped global protein dynamics.

Sas_analyzer software for small-angle X-ray scattering data treatment

New approaches to the analysis of small-angle X-ray scattering data from nanoscale systems based on the optimization and direct multiple shooting methods are presented. A program is developed, which bears on these new approaches and allows a user to model small-angle X-ray diffraction data, introduce collimation corrections, and analyze dispersions in the samples. The program results for a number of typical nanosized systems (sols, catalysts) are reported and the comparison with currently available programs for small-angle data processing is presented.

Aperiodic Crystals at the Mesoscale

Materials with mesoscale structural characteristics have attracted great attention across the fields of chemistry, physics, and materials science. A typical example is mesoporous silica, which are synthesized in water/surfactant/silica systems, and has well-defined mesopores resulting in high surface area. Mesoporous silicas have two defining structural characteristics: (i) disorder at the atomic scale, i.e. only short-range order; and (ii) distinct order at the mesoscale, i.e. long-range order. Atomic-scale structural characterization by common diffraction techniques, such as X-ray single crystal diffraction, is challenging for these partially ordered materials. This is because of the difficulty in obtaining large (> 10 µm) single crystals, and because large-distance periodic features cause diffraction intensities to fall off rapidly with scattering angle, so that only limited small-angle data are available. On the other hand, transmission electron microscopy (TEM) is a powerful tool for structural characterization at the mesoscale level due to the stronger interaction of electrons with matter compared to X-rays, enabling the use of very small crystals. In particular, high-resolution TEM (HRTEM) images give the phase and the amplitude of the crystal structure factors experimentally, leading to a 3D structural model by electron crystallography. Cage-type anionic-surfactant-templated mesoporous silicas display rich structural diversity. Among them, cage-type mesoporous silica with tetrahedrally close-packed (TCP) structures can be described by four types of polyhedra, 5^12, 5^12 6^2, 5^12 6^3, and 5^12 6^4.[1] A variety of structural polymorph have been observed and characterized by TEM. Their structures show a close resemblance to the Frank-Kasper phases, which are well known in intermetallic compounds. We found mesoporous silica with dodecagonal quasicrystalline ordering as one of the TCP structures (Figure).[2] In this presentation, I will discuss structural characterization of aperiodic crystals at the mesoscale, such as mesoporous silicas and binary colloidal crystals, by electron microscopy.

Comprehensive diagnostics of the dimensional features of gold nanoparticles formed under the UV reduction of HAuCl4 in chitosan solutions

The kinetics of formation of gold nanoparticles in chitosan solutions doped with HAuCl4 under the UV-induced reduction of Au3+ and their dimensional features and aggregative stability are studied via optical spectroscopy, small-angle X-ray scattering, and high-resolution transmission electron microscopy. The nanoparticles are spherical in shape and are characterized by a narrow size distribution. The electron microscopy and small-angle radiography data are quantitatively almost identical. A linear correlation between the average size of Au nanoparticles and the position of their plasmon absorption maximum is found. A high aggregative stability of nanoparticles in chitosan solutions is revealed.

Application of Image Enhancement Algorithm in Multi-Phase Flow CT System

In this paper, image enhancement algorithm is applied to multi-phase CT system imaging. Aiming at artifact imaging of multiphase flow CT system image reconstruction, this paper uses image enhancement algorithm to enhance the reconstructed image. The simulation results prove that with a small amount projection angle data about reconstruction it can also get clear images by using image enhancement algorithm processing and also remove artifacts for reconstructed image. It is efficient to shorten the multi-phase CT system image reconstruction data collection time, and benefit to analysis multi-phase transient flow pattern.

A simple procedure to evaluate the efficiency of bio-macromolecular rigid-body refinement by small-angle scattering

A simple and rapid procedure is presented that enables evaluation and visualization of refinement efficiency for bio-macromolecular complexes consisting of two subunits in a given orientation by using small-angle scattering. Subunit orientations within a complex can be provided in practice by NMR residual dipolar couplings, an approach that has been combined with increasing success to complement small-angle data. The procedure is illustrated by applying it to several systems composed of two simple geometric bodies (ellipsoids) and to protein complexes from the protein data bank that vary in subunit size and anisometry. The effects of the experimental small-angle scattering range (Q-range) and data noise level on the refinement efficiency are investigated and discussed. The procedure can be used in two ways: (1) either as a quick preliminary test to probe the refinement capacity expected for a given bio-macromolecular complex prior to sophisticated and time-consuming experiments and data analysis, or (2) as an a posteriori check of the stability and accuracy of a refined model and for illustration of the residual degrees of freedom of the subunit positions that are in agreement with both small-angle data and restraints on subunit orientation (as provided, e.g., by NMR).

Elastic and inelastic scattering of 7Li + 18O versus 7Li + 16O

Angular distributions of the 7Li + 18O elastic and inelastic scattering were measured at the energy E lab ( 18O) = 114 MeV (32 MeV c.m.) in inverse kinematics. This technique allowed both small and large angle data to be collected simultaneously. The data were analyzed within the optical model and coupled-reaction-channels method to determine the potential parameters of 7Li + 18O scattering and reaction channels dominating the scattering. 18O inelastic scattering deformation parameters were obtained. The present data show that the 7Li + 18O system has a much stronger absorption when compared to previously measured 7Li + 16O data. The derived optical model parameters clearly show the scattering difference between two systems.

The scattering of 40 eV electrons from magnesium: a polarization correlation study for the31Pstate and differential cross sections for elastic scattering and excitation of the 31P and33Pstates

Excitation of the 31Pstate of magnesium by 40 eV electrons has been studied experimentallyusing the polarized photon-scattered electron correlation method over awide range of scattering angles (10°–120°).Measured Stokes parameters are consistent with the small angle (≤20°) data ofBrunger et al (1989 J. Phys. B: At. Mol. Opt. Phys. 22 1431–32). The measured linear Stokesparameters, and the circular polarization calculated from theseparameters, assuming coherent excitation, are generally wellproduced by recent theoretical models, convergent close coupling,R-matrixwith pseudo states, relativistic distorted wave and first-order many-bodytheory. Despite extensive testing, directly measured circular polarizationdata yielded low values at most scattering angles beyond 20°.Differential cross sections for elastic scattering and excitation of the 31P and33Pstates were also measured over the angular range 10°–140° andcompared with theoretical predictions.

Crystalline Structure and Morphology in Nylon-12: A Small- and Wide-Angle X-ray Scattering Study

Simultaneous small- and wide-angle X-ray scattering has been employed to monitor the temperature dependence of the crystalline structure and morphology of nylon-12. Wide-angle measurements reveal that the α‘-phase is a stable high-temperature crystalline phase. Upon cooling, a crystalline transition takes place from the α‘-form into the hexagonal γ-phase. The small-angle data indicate at this point a discontinuous change in the density. At low temperatures, two crystal reflections occur at wide angles. This is interpreted as a monoclinic or an orthorhombic structure, which evolves from the hexagonal structure of the γ-form by an anisotropic thermal expansion. The evolution of the crystalline thickness during cooling and heating suggests the occurrences of partial surface crystallization and melting. This effect is superimposed on the transition α‘ ↔ γ and leads to crystal thickening and thinning during cooling and heating, respectively. The transition from γ to α‘ with increasing temperature arises from a “one-dimensional-melting” type of rupture between the hydrogen-bonded sheets. Finally, fast quenching from the melt results in the γ‘-phase, which transforms upon annealing into either the γ- or the α‘-polymorph. This process proceeds most probably through a melting and recrystallization process.

Direct imaging of the pores and cages of three-dimensional mesoporous materials

Mesostructured composite materials, with features ranging from 20 to 500 A in size, are obtained by the kinetically controlled competitive assembly of organic and inorganic species into nanostructured domains. Short-range order is limited, and long-range order is determined by weak forces such as van der Waals or hydrogen-bonding. Three-dimensional mesoporous materials obtained by removing the organic phase are of particular interest for applications such as catalysis and chemical sensing or separation, for which structural features such as cavity shape, connectivity and ordered bimodal porosity are critical. But atomic-scale structural characterization by the usual diffraction techniques is challenging for these partially ordered materials because of the difficulty in obtaining large (> 10 microm) single crystals, and because large repeat spacings cause diffraction intensities to fall off rapidly with scattering angle so that only limited small-angle data are available. Here we present a general approach for the direct determination of three-dimensional mesoporous structures by electron microscopy. The structure solutions are obtained uniquely without pre-assumed models or parametrization. We report high-resolution details of cage and pore structures of periodically ordered mesoporous materials, which reveal a highly ordered dual micro- and mesoscale pore structure.

Structure of polymerizable lipid bilayers VII: lateral organization of diacetylenic phosphatidylcholines with short proximal acyi chains

As an extension of recent results (Rhodes, Xu and Bittman (1992) Biochim. Biophys. Acta 1128, 93; Hui, Xu and Bittman (1992) Langmuir 8, 2724) with a C18 diacetylenic phosphatidylcholine, bilayers of 1,2-bis(pentacosa-4,6-diynoyl)- sn-glycero-3-phosphocholine (C25) were investigated using X-ray diffraction on multibilayers and electron diffraction on Langmuir-Blodgett deposited bilayers. Monolayers of this lipid form solid (gel phase) domains at π > 14 mN/m. Electron diffraction data indicated that the chain spacing in these domains is 4.25 Å and that the chains are tilted at angle of ~ 35° relave to the bilayer plane. Wide angle data from X-ray diffraction experiments indicated a similar spacing and chain tilt. Small angle data showed that the lamellar repeat was 70 Å at high humidity and ⩽ 60 Å at low humidity. The bilayer electron density profiles indicated a bilayer structure with no interdigitation. High angle reflections indicate that the principal acyl chain repeat is preserved as a function of hydration but some rearrangement occurs for other reflections. The ~ 10 Å reflection corresponding to the headgroup spacing previously observed with C18-diacetylenic phosphatidylcholine bilayers was not observed. The results are interpreted in terms of a packing model and possible limitations or constraints to the polymerization process.

Conditions for the existence of a reentrant solid phase in a sheared atomic fluid.

A nonequilibrium molecular-dynamics method is proposed to simulate the behavior of simple fluids under high shear rates. A thermostat that makes no assumptions regarding the form of the streaming velocity of the fluid is introduced. Simulations are carried out for a Weeks-Chandler-Andersen dense liquid. With the form of the streaming velocity partially or wholly constrained, we find evidence for a reentrant solid or string phase, but the phase disappears if constraints are removed. Small-angle neutron-scattering data from a sheared colloidal suspension are presented. There is no evidence of a steady-state shear-induced structure in the suspension.

A measurement of the total cross section at √s= 1800GeV

The p p differential elastic scattering cross section was measured at √ s =1800 GeV, using an improved accelerator luminosity determination and CDF small angle data in the range of 0.05 ≤ t ≤ 0.2( GeV / c ) 2 . By extrapolating the differential cross sections to t=0 and using the optical theorem we obtain a total cross section of σ tot ( pp ) = 72.0±3.6 mb. This result is preliminary in the sense that we expect to further reduce the systematic error on the optical point.

A measurement of the pp total cross section at √s = 1800 GeV

The pp differential elastic scattering cross section was measured at √s = 1800 GeV, using an improved accelerator luminositydetermination and CDF small angle data in the range of 0.05 ≤ t ≤ 0.2( GeV/c) 2. By extrapolating the differential cross sections to t=0 and using the optical theorem we obtain a total cross section of σ tot(pp) = 72.0±3.6 mb. This result is preliminary in the sense that we expect to further reduce the systematic error on the optical point.

Mass dependence of high-energy pion double charge exchange.

The mass dependence of cross sections for double-isobaric-analog states from pion-induced double-charge-exchange reactions is examined with small-angle data taken at 450 and 500 MeV incident pion energies for several targets. New ({pi}{sup +},{pi}{sup {minus}}) cross sections are reported for {sup 26}Mg, {sup 46,50}Ti, {sup 54,56}Fe, {sup 52}Cr, {sup 80}Se, {sup 90}Zr, {sup 197}Au, and {sup 208}Pb. The ({ital f}{sub 7/2}){sup {ital n}} data are fitted to a two-amplitude model which contains expressions for cross sections for transitions to the DIAS and to nonanalog ground states in the residual nucleus.