Small Angle Range Research Articles

A small-angle x-ray scattering system with a vertical layout.

A small-angle x-ray scattering (SAXS) system with a vertical layout (V-SAXS) has been designed and constructed for in situ detection on nanostructures, which is well suitable for in situ study on self-assembly of nanoparticles at liquid interface and polymer processing. A steel-tower frame on a reinforced basement is built as the supporting skeleton for scattering beam path and detector platform, ensuring the system a high working stability and a high operating accuracy. A micro-focus x-ray source combining parabolic three-dimensional multi-layer mirror and scatteringless collimation system provides a highly parallel beam, which allows us to detect the very small angle range. With a sample-to-detector distance of 7 m, the largest measurable length scale is 420 nm in real space. With a large sample zone, it is possible to install different experimental setups such as film stretching machine, which makes the system perfect to follow the microstructures evolution of materials during processing. The capability of the V-SAXS on in situ study is tested with a drying experiment of a free latex droplet, which confirms our initial design.

Feature extraction of micro-motion frequency and the maximum wobble angle in a small range of missile warhead based on micro-Doppler effect

Micro-Doppler effect is induced by the micro-motion dynamics of the radar target itself or any structure on the target. In this paper, a simplified cone-shaped model for ballistic missile warhead with micro-nutation is established, followed by the theoretical formula of micro-nutation is derived. It is confirmed that the theoretical results are identical to simulation results by using short-time Fourier transform. Then we propose a new method for nutation period extraction via signature maximum energy fitting based on empirical mode decomposition and short-time Fourier transform. The maximum wobble angle is also extracted by distance approximate approach in a small range of wobble angle, which is combined with the maximum likelihood estimation. By the simulation studies, it is shown that these two feature extraction methods are both valid even with low signal-to-noise ratio.

Venus’ clouds as inferred from the phase curves acquired by IR1 and IR2 on board Akatsuki

We present phase curves for Venus in the 1–2μm wavelength region, acquired with IR1 and IR2 on board Akatsuki (February–March 2011). A substantial discrepancy with the previously-published curves was found in the small phase angle range (0–30°). Through analysis by radiative-transfer computation, it was found that the visibility of larger (∼1μm or larger) cloud particles was significantly higher than in the standard cloud model. Although the cause is unknown, this may be related to the recently reported increase in the abundance of SO2 in the upper atmosphere. It was also found that the cloud top is located at ∼75km and that 1-μm particles exist above the cloud, both of these results being consistent with recent studies based on the Venus Express observations in 2006–2008. Further monitoring, including photometry for phase curves, polarimetry for aerosol properties, spectroscopy for SO2 abundance, and cloud opacity measurements in the near-infrared windows, is required in order to understand the mechanism of this large-scale change.

THE Hα PROFILES OF Be SHELL STARS

A new set of theoretical Hα emission line profiles of Be stars has been computed using the code BERAY, which solves the transfer equation along a series of rays passing through the star+disk system, representing an improved treatment over earlier work done by the authors. The new profiles were compared with the previous work, and general trends (such as line profile shapes and correlations between line equivalent widths as a function of initial density ρ0 and power law index n) were recovered. Additionally, BERAY was employed to model the spectra of eight well-known Be shell stars. Some degeneracy was found in the choice of model parameters, highlighting the need to employ alternate observables to constrain the models. However, the inclination angle of the model seemed relatively insensitive to the choices of other parameters, and we show that, with our models, only a very small range of inclination angles can adequately reproduce the observations. Five of our eight targets were found to have inclination angles of 70° or higher, and two more were found to have inclination angles of 67° and 65°. The observation of one target—4 Aquilae—could only be reproduced by models created at an inclination angle of approximately 45°.

Interpretation of small-angle scattering of block copolymer/nanoparticle blends using random phase approximation

The scattering characteristics of block copolymer (BCP)/nanoparticle (NP) blend systems are analyzed in the weak segregation limit using random phase approximation (RPA). The scattering function is established and shown to adequately capture reported data of small-angle neutron scattering in poly(norbornene-b -d-norbornene dicarboxylic acid)/ Fe3O4 nanoparticle blend systems over the entire small-angle range for a variety of BCP and NP compositions. Besides predicting the relevant length scales of microstructure formation, the RPA analysis reveals the increase of segregation in the BCP system upon NP addition. The insight into the thermodynamics of microstructure formation in BCP/NP blend systems that is provided by the RPA analysis should be a valuable asset for the design of BCP-based microstructured hybrid materials with predetermined structure and properties.

Limited-angle tomography applied to biological objects

Optical limited-angle tomography is strongly required in biological applications, as often there is an access to projections gathered from a small angle range. Choosing a reconstruction algorithm among many available is always a tradeoff between speed of calculation and quality of reconstruction. In this paper we present the studies how the a priori information about object’s geometry influences efficiency of the Data Replenishment Algorithm. The analysis is based on tomographic reconstruction of real biological cell of human malignant lymphoma. Full Text: PDF References S. Kou, C. Sheppard, "Image formation in holographic tomography", Opt. Lett. 33, 2362 (2008). CrossRef J. Hsieh, Computed Tomography Principles, Design, Artifacts, and Recent Advances (Wiley 2009). S. Isikman et al., "Lens-free optical tomographic microscope with a large imaging volume on a chip", P. Natl. Acad. Sci. USA 108, 7296 (2011). CrossRef S. Vertu, E. Maeda, J. Flügge, J. Delaunay, O. Haeberlé, "Comparison of resolution in tomographic diffractive microscopy using combinations of sample rotation and illumination rotation", Proc. SPIE 7904 (2011). CrossRef A. Likhachov, "Projection data replenishment algorithm for limited angle tomography", Optoelectron. Instrum. Data Process. 45, 55 (2009). DirectLink R. Gordon, "A tutorial on art (algebraic reconstruction techniques)", IEEE T. Nucl. Sci. 21, 78 (1974). CrossRef A. Andersen, A. Kak, "Simultaneous Algebraic Reconstruction Technique (SART): A Superior Implementation of the Art Algorithm", Ultrasonic Imaging 6, 81 (1984). CrossRef D. Verhoeven, "Limited-data computed tomography algorithms for the physical sciences", Appl. Optics 32, 3736 (1993). CrossRef J. Fessler, B. Sutton, "Nonuniform fast Fourier transforms using min-max interpolation", IEEE T. Signal Proces. 51, 560 (2003). CrossRef Z. Wang, A. Bovik, "A universal image quality index", IEEE Signal Proc. Let. 9, 81 (2002). CrossRef M. Kujawińska et al., "Problems and Solutions in Tomographic Analysis of Phase Biological Objects", Fringe 2013, 671 (2013) CrossRef

Research on the torsional fretting behavior of the head–neck interface of artificial hip joint

The torsional fretting behavior of the head–neck interface of artificial hip joint composed of Ti6Al4V and CoCrMo was investigated. The torsional fretting mechanisms were evaluated by experiments at various angular displacement amplitudes. The friction coefficient for the head–neck interface was calculated using contact mechanics. The head–neck interface model was established in accordance with the artificial hip joint head–neck size. The conical angle and diameter of the artificial hip joint head were optimized using data derived from the finite element method (FEM). The results indicate that torsional fretting changes from partial slip regime to slip regime with increasing angular displacement amplitude. Friction torque, friction dissipated energy, and the friction coefficient increase with increasing angular displacement amplitude and wear intensifies. Finite element simulation results demonstrate that self-locking occurs in the head–neck interface of artificial hip joint more readily at small conical angles. The head–neck interface is least susceptible to fretting when the conical angle is 5°42′30″. Relative displacement and contact stress can be reduced by appropriately increasing the conical angle within a small angle range and increasing the artificial hip joint head diameter, which can decrease fretting wear.

Acoustic Wave Equation Modeling with New Time‐Space Domain Finite Difference Operators

AbstractNumerical simulation of acoustic wave equation is widely used to theoretically synthesize seismograms, and also constitutes the basis of the reverse time migration. Under some stability conditions, grid dispersion often exists because of the discretization of time and spatial derivatives in wave equations. How to suppress the grid dispersion is therefore a key problem for finite difference approaches. Time‐space domain methods using plane‐wave theory and Taylor series expansion are proposed to suppress grid dispersion recently. However, these methods can only preserve the wavefield in a small range of frequencies and angles of propagation. To further suppress the grid dispersion, we propose to preserve the grid dispersion relationship in a large range of frequencies and angles of propagation. Dispersion analysis and seismic numerical simulations demonstrate the effectiveness of the proposed method.

Study of Vehicle Sideslip Angle Real-Time Estimation Method

In the vehicle stability control and other active safety systems, vehicle sideslip angle real-time estimation is necessary. However, the direct measurement of sideslip angle is more difficult or too costly, so it is often used in estimating methods. The vehicle sideslip angle of closed-loop Luenberger observer and Kalman observer were constructed based on two degrees of freedom bicycle model, as well as the direct integration method for large sideslip angle conditions. The comparative study showed that Kalman filtering estimation method and Luenberger estimation methods have better estimation accuracy in small slip angle range.

Radiative decay engineering 7: Tamm state-coupled emission using a hybrid plasmonic–photonic structure

There is a continuing need to increase the brightness and photostability of fluorophores for use in biotechnology, medical diagnostics, and cell imaging. One approach developed during the past decade is to use metallic surfaces and nanostructures. It is now known that excited state fluorophores display interactions with surface plasmons, which can increase the radiative decay rates, modify the spatial distribution of emission, and result in directional emission. One important example is surface plasmon-coupled emission (SPCE). In this phenomenon, the fluorophores at close distances from a thin metal film, typically silver, display emission over a small range of angles into the substrate. A disadvantage of SPCE is that the emission occurs at large angles relative to the surface normal and at angles that are larger than the critical angle for the glass substrate. The large angles make it difficult to collect all of the coupled emission and have prevented the use of SPCE with high-throughput and/or array applications. In the current article, we describe a simple multilayer metal–dielectric structure that allows excitation with light that is perpendicular (normal) to the plane and provides emission within a narrow angular distribution that is normal to the plane. This structure consists of a thin silver film on top of a multilayer dielectric Bragg grating, with no nanoscale features except for the metal or dielectric layer thicknesses. Our structure is designed to support optical Tamm states, which are trapped electromagnetic modes between the metal film and the underlying Bragg grating. We used simulations with the transfer matrix method to understand the optical properties of Tamm states and localization of the modes or electric fields in the structure. Tamm states can exist with zero in-plane wavevector components and can be created without the use of a coupling prism. We show that fluorophores on top of the metal film can interact with the Tamm state under the metal film and display Tamm state-coupled emission (TSCE). In contrast to SPCE, the Tamm states can display either S or P polarization. The TSCE angle is highly sensitive to wavelength, which suggests the use of Tamm structures to provide both directional emission and wavelength dispersion. Metallic structures can modify fluorophore decay rates but also have high losses. Photonic crystals have low losses but may lack the enhanced light-induced fields near metals. The combination of plasmonic and photonic structures offers the opportunity for radiative decay engineering to design new formats for clinical testing and other fluorescence-based applications.

Studies on microwave-irradiated kopak cotton fibers (Bombax ceiba): using SAXS technique

Microwave energy at a frequency of 2450 MHz was used to irradiate Bombax ceiba cotton (kopak fibers) samples for different intervals of time. These samples were studied using small angle X-ray scattering (SAXS) method which gives information about the structure of the fiber on a scale of about 700 Ǻ. Using this method, variation in scattered intensity with angles from 0.3° to 2.5° has been measured for the fibers of cotton with and without microwave irradiation and compared with that predicted by the linear paracrystalline model. In these samples, exponential distribution of phase lengths of the measured and predicted scattering is in good agreement with each other except for a very small range of angles on the low-angle side of the peak intensity. The method enabled quantitative parameters describing morphology of the two phases, amorphous and crystalline, consistent with the SAXS intensity distribution. For a given type of distribution function, five parameters describing the model were chosen on a stepping procedure so that the final parameters give the best fit between the calculated distribution from the model and that observed experimentally. This was done by minimizing the statistical goodness-of-fit parameter chi-square. It is observed that there are significant changes in the distribution of phase lengths due to microwave irradiation of fibers.

Obtaining High Fringe Precision in Self-Mixing Interference Using a Simple External Reflecting Mirror

Based on the study of laser diode self-mixing interference effects, a simple and effective method that can improve fringe precision is presented. By employing an external reflecting mirror, theoretical and experimental results show an assured increase about two or three times in the resolution of the displacement measurement, which means a fringe shift is corresponding to a near 1/6 wavelength displacement of the target. At a small angle range, when the fringe precision is not fixed, this method can still have a relative high precision and a large measurement range. The maximum measurable displacement and error of precision are also discussed.

Design and analysis of guided-mode resonance filter containing an absentee layer with an antireflective surface

A design approach to guided-mode resonance filter containing an absentee layer with an antireflective surface is presented. This design approach is reliable for the design and analysis of guided-mode resonance filter containing an absentee layer with an antireflective surface at an arbitrary incidence. The antireflection condition of guided-mode resonance filter containing an absentee layer is obtained. For the absentee layer with a fixed optical thickness, the resonance wavelength can be selected, with the low-sideband features and the filter linewidth kept almost the same by using different materials. In addition, the resonance wavelength and its linewidth can be tuned almost linearly in a broad spectral band as the incident angle is varied due to high angular tolerance of the antireflection features of the filter in the range of small angle.

Iterative Breast Tomosynthesis Image Reconstruction

In digital tomosynthesis imaging, multiple projections of an object are obtained along a small range of different incident angles in order to reconstruct a pseudo-3D representation of the object. In this paper we discuss a mathematical model for polyenergetic digital breast tomosynthesis image reconstruction that explicitly takes into account various materials composing the object and the polyenergetic nature of the x-ray beam. Our model allows for computing weight fractions of the individual materials that make up the object, which can then be used to reconstruct pseudo-3D images. The reconstruction process requires solving a large-scale inverse problem, which is done with a gradient descent iteration. Regularization is enforced by truncating the iteration. The mathematical model is described in detail, as is an efficient approach to compute the gradient of the objective function. The effectiveness of our approach is illustrated with real data taken of an object with known materials that simulates an actual breast.

Winds, sea levels and North Atlantic Oscillation (NAO) influences: An evaluation

This work presents the analysis of fifteen years (1993 to 2007 inclusive) MetOffice wind data for the Bristol Channel/Severn Estuary. Data from the Turbot Bank Buoy, located within the open waters of the Bristol Channel, showed significant reducing trends in monthly mean and maximum extreme wind speeds. Coupled with significant falling extreme sea level trends over the same time period, and direct correlation between wind speed and sea level, the increased storminess experienced during the latter half of the twentieth century seems not to have continued into the first decade of the twenty-first century. Wind speeds and directions between 1993 and 2002 inclusive at Turbot Bank Buoy were found to be significantly higher than those measured at the relatively nearby Rhoose land based station (Paired t test: tcalc=87.74, df=9, p<0.01 and tcalc=46.6, df=9, p<0.01 respectively). This highlights problems in using land based wind records to represent sea conditions, as well as using one location as representative of conditions along a coastline. Analysis further showed a small range of annual mean wind angles (circa 180° to 210° true). There was a significant regression between wind speed and NAO Index, given by 0.33±0.06knots/NAO unit (p=0.000). This was more important during positive NAO phases, as wind speeds reduced during negative phases. Regression also indicated a direct positive relationship between NAO Index and wind direction (15.7±7.5°/NAO unit; p=0.05), where higher wind angles are linked to a rising NAO. Therefore, results have major implications for morphological response to wind (speed and direction), sea level (mean and extreme) and NAO Index (positive and negative). Conditions are unlikely to be unique to this coastline and it is suggested that similar analyses are replicated elsewhere to improve understanding and characterisation of uncertainty.

TOF-SEMSANS—Time-of-flight spin-echo modulated small-angle neutron scattering

We report on measurements of spatial beam modulation of a polarized neutron beam induced by triangular precession regions in time-of-flight mode and the application of this novel technique spin-echo modulated small-angle neutron scattering (SEMSANS) to small-angle neutron scattering in the very small angle range. It is shown that this method can be implemented straight-forwardly in order to extend the accessible size range of structures to be investigated by SANS towards a microscopic scale by applying a divergent beam and measuring the real space correlation function. The novel approach of SEMSANS enables the application of sophisticated sample environment and measurements of magnetic samples (in contrast to the analogue method SESANS).

Using a grating analyser for SEMSANS investigations in the very small angle range

Spin-echo modulation small-angle neutron scattering (SEMSANS) is based on the detection of spatial beam modulation, which is induced by triangular spin echo precession regions and subsequent spin analyses. In order to detect such signal and exploit it for small angle scattering investigations neutron detection with sub-millimeter spatial resolution is required. Here an approach is reported where instead of a position sensitive detector an absorption grating is used to analyze the beam modulation stepwise. The spin-echo length scan in this case is performed by varying the sample-to-detector distance. The real space correlation functions of reference sample structures in the range 10(2) nm, i.e. giving rise to small-angle scattering in the very small-angle range, are recorded and analyzed successfully. (C) 2012 Elsevier B.V. All rights reserved. (Less)

Computer simulation of layer‐by‐layer sputtering at grazing low‐energy ion‐surface interactions

The peculiarities of sputtering processes at low‐energy Ne grazing ion bombardment of Si(001), SiC(001) and Cu3Au(001) surfaces and their possible application for the surface modification have been studied by computer simulation. Sputtering yields in the primary knock‐on recoil atoms regime versus the initial energy of incident ions (0.5–5 keV) and angle of incidence (0–30°) with respect to the target surface have been calculated. It was shown that in the case of grazing ion bombardment, the layer‐by‐layer sputtering is possible, and its optimum is observed within the small angular range of the glancing angles near the threshold sputtering angle. Comparative studies of layer‐by‐layer sputtering for Si(001) and SiC(001) surfaces versus the initial energy of incident ions as well as an effective sputtering and sputtering threshold are discussed. Copyright © 2012 John Wiley &amp; Sons, Ltd.

얼굴 모델간 선형변환을 이용한 정밀한 얼굴 포즈추정 및 포즈합성

This paper presents a method that estimates face pose for a given face image and synthesizes any posed face images using Active Appearance Model(AAM). The AAM that having been successfully applied to various applications is an example-based learning model and learns the variations of training examples. However, with a single model, it is difficult to handle large pose variations of face images. This paper proposes to build a model covering only a small range of angle for each pose. Then, with a proper model for a given face image, we can achieve accurate pose estimation and synthesis. In case of the model used for pose estimation was not trained with the angle to synthesize, we solve this problem by training the linear relationship between the models in advance. In the experiments on Yale B public face database, we present the accurate pose estimation and pose synthesis results. For our face database having large pose variations, we demonstrate successful frontal pose synthesis results.

Laminar mesoporous structure of modified montmorillonite clays and its formation mechanism

Zr-pillared clays were prepared by heating and ultrasonic methods in intercalation process. The resultants were characterized by XRD, N2 adsorption-desorption, SEM, and TG/DTA analysis. Ultrasonic technology accelerated the pillaring process effectively and obtained better ordered structure than by heating method. The specific surface area and pore volume of the Zr-pillared clays increased by about 13 and 3 times respectively. Rare earth metal (Ce) was introduced into Zr-pillared clays by co-intercalation and dipping method. The specific surface area was increased by co-intercalation approach, but it was decreased dramatically by dipping method. Thermal stability of Ce modified samples prepared by co-intercalation method was enhanced in comparison with Zr-pillared clays. Modification mechanism and “corrugation-like” structural mode of intercalation process was proposed basing on the double XRD peaks in small-angle range of pillared clays, which was related to the deformation of silicate layer.