Source Spot Research Articles

A Novel Stationary CT Scheme Based on High-Density X-Ray Sources Device

With the introduction of cold electron sources such as nanotubes, X-ray sources became small in size so that many sources are installed in array to form stationary CT, which brings benefits of simplicity in mechanism and fast response. However, the nanotube-based X-ray source is still singly packaged and hence density of X-ray sources is limited, which introduces severe sparse-view artifacts and could not be used in practice. With the invention of X-ray sources device based on ZnO nanowires as cold electron emitters, a large amount of X-ray sources is first integrated in a flat panel device. In this study, we design a stationary CT architecture using high-density sources devices, called HD-SCT, and develop corresponding reconstruction algorithm. Specifically, several flat panel detectors and X-ray sources devices are spliced together to form a source-detector plate. Multiple source-detector plates are organized as a polygon that encloses object to complete CT scanning. In HD-SCT, X-ray sources are close to object which can significantly decrease CT device volume. The X-ray beam emitted by each source just cover part of object and the spot sources alternately light to completely scan object. Simultaneously, we propose a reconstruction method for the specific configuration which adopts an iterative algorithm to resolve the reconstruction based on alterative part projections, as well as a novel correction process of projection completion for the shadowed area of placing X-ray source devices. To validate the design of the proposed HD-SCT, we execute a series of simulation experiments, which show that the proposed HD-SCT and corresponding reconstruction method effectively remove the artifacts caused by the embed X-ray source device. The results also disclose that with the increase of density of X-ray sources, the resolution of reconstruction has been dramatically improved, which demonstrates the practical value of introducing high-density X-ray sources device into stationary CT design.

Measurement of Thermal Cycle at Multi-Pass Layer Build-Up with Different Travel Path Strategies during DLMD Process

The shape of the parts, created by the technology of direct laser metal deposition (DLMD), is influenced by various parameters, for example, the power and diameter of the laser source spot. The contribution of energy from the laser affects the temperature distribution in the formed layers. The changing temperature in the working area entails a change in the geometry of the layers and affects the stability of the process. In this paper, experiments on the measurement of temperature cycles in the DLMD process with different directions of the filling track are carried out. An infrared camera was used to measure thermal cycles. The correspondence table between the intensity of thermal radiation of the material and the absolute temperature was developed. The experiments are carried out with the filler material 316L. The effect of the maximum temperature on the layer height is shown, and thermal cycles in the formation of layers for different filling strategies are presented.

A numerical simulation of the generation and evolution of nonlinear internal waves across the Kara Strait

Nonlinear internal waves (NIWs) are ubiquitous around the Kara Sea, a part of the Arctic Ocean that is north of Siberia. Three hot spot sources for internal waves, one of which is the Kara Strait, have been identified based on Envisat ASAR. The generation and evolution of the NIWs through the interactions of the tide and topography across the strait is studied based on a nonhydrostatic numerical model. The model captures most wave characteristics shown by satellite data. A typical inter-packets distance on the Barents Sea side is about 25 km in summer, with a phase speed about 0.65 m/s. A northward background current may intensify the accumulation of energy during generation, but it has little influence on the other properties of the generated waves. The single internal solitary wave (ISW) structure is a special phenomenon that follows major wave trains, with a distance about 5–8 km. This wave is generated with the leading wave packets during the same tidal period. When a steady current toward the Kara Sea is included, the basic generation process is similar, but the waves toward the Kara Sea weaken and display an internal bore-like structure with smaller amplitude than in the control experiment. In winter, due to the growth of sea ice, stratification across the Kara Strait is mainly determined by the salinity, with an almost uniform temperature close to freezing. A pycnocline deepens near the middle of the water depth (Barents Sea side), and the NIWs process is not as important as the NIWs process in summer. There is no fission process during the simulation.

Experimental Study of the Effect of Light Source Spot Size on Measure Error of PSD

The energy distribution of the incident light spot on position-sensitive detector (PSD) screen is uneven and the output coordinate value is the energy centre of the light spot. Measurement error caused by the deviation between the geometric and gravity centre of the light spot will occur. The deviation will increase with the increase of the diameter of the light spot. There is no quantitative research on the position error caused by the changes of the light spot diameter and the distance from the light spot to the PSD. To evaluate the magnitude of the error, the infrared spotlight is selected as the target light. The changing pattern that the spot diameter varies with the distance between the light source and lens is studied. Additionally, the effect of the spot size on the PSD measure error is studied. The research provides reference for error evaluation of the distance and position detection of PSD. [Submitted 5 July 2017; Accepted 24 December 2017]

Experimental study of the effect of light source spot size on measure error of PSD

Experimental study of the effect of light source spot size on measure error of PSD

Multi-Beam Metasurface Antenna by Combining Phase Gradients and Coding Sequences

In this paper, we propose a strategy to achieve a single-feed multi-beam metasurface antenna by combining phase gradient and coding sequence. Theoretically, the multi-beam antennas with various far-field patterns can be realized via superimposing different kinds of phase coding sequences. As three proof-of-concepts, the 0101.../0101...coding sequence, chessboard coding sequence, and 1-bit sector coding sequence are selected to design double-beam, four-beam, and eight-beam circular-polarized reflector antennas, respectively. Furthermore, the four-beam reflector antenna is fabricated and measured to demonstrate the feasibility of our strategy. The fabricated antenna can produce four perfect pencil-shaped beams in a wide frequency range from 11 to 13 GHz. At central frequency, the realized gain is about 19.9 dB and the axial ratio is lower than 3 dB. Moreover, the circular polarization state of the reflective beams is consistent with the polarization state of spot source, which differs from the reflector antennas based on the polarization-insensitive unit cells. This paper connects the multi-beam patterns with binary digits, which provide the potential for reconfiguring the multi-beam patterns by computer programs.

Preliminary Experimentation of Fast Neutron Radiography with D-T Neutron Generator at BARC

An experimental study on fast neutron radiography (FNR) has been carried out using a laboratory based D-T neutron generator facility at Bhabha Atomic Research Centre (BARC) and initial results are presented. The aim was to develop an FNR system with a moderate intensity neutron source for imaging of specimen containing mixed low-Z and high-Z materials. The experimental set-up consists of a D-T neutron generator, collimator and an EMCCD camera based imaging system. Experiments were carried out with the neutron generator having a source strength of about 2 × 109 n/s and source spot size of 20 mm. To obtain optimum image quality with such a moderate neutron yield, a collimator has been designed having an inlet aperture of 10 mm and an L/D of 43. The imaging system was kept at an optimum distance from the collimator and various test samples of materials ranging from low Z to high Z were imaged. Thick samples in step wedge form, hole features in step wedge of polyethylene, mild steel and lead were imaged and analysed. Also a test sample of a low Z material (HDPE) with a hole placed behind a thick Pb was imaged to study the effect of thickness of high Z material on image quality with fast neutrons. The initial results emphasizes that a moderate yield D-T neutron generator based fast neutron radiography system with EMCCD camera could be deployed for field applications yielding moderate image quality to obtain first hand information of the investigated samples.

A multi-functional vortex beam generator based on transparent anisotropic metasurface

Abstract Vortex beam generators are increasingly in demand for their enormous potential in improving communication capability. Along with the continuous integration of electronic product, devices with single function cannotsatisfy the requirements of the people. Here, by employing an anisotropic metasurface (MS), we propose a transparent multi-functional vortex beam generator to obtain vortex beams with reconfigurable polarization status. An anisotropic element is firstly optimized to control x- and y-polarized wave independently, and then is applied to assemble a vortex beam generator that is not only able to convert spherical wavefront into a vortex one but also able to transform linearly polarized mode into the circular polarized counterpart. Interestingly, the polarized status of the generated vortex beam changes from x-polarization to left hand circularly polarization (LHCP) to y-polarization and finally to right hand circularly polarization (RHCP) when the spot source is rotated with different angles. For verification, the prototype of the practical configuration is fabricated and measured. Coinciding well with the simulated results, the measured ones show that linearly polarized spherical wave has been converted into LHCP or RHCP vortex beams with operating efficiency of 85.8% or 83.3% respectively.

Assessing Quasi‐Periodicities in Jovian X‐Ray Emissions: Techniques and Heritage Survey

AbstractJupiter's auroral X‐rays are rather mysterious, with an unknown driver, and several previous reports of individual cases of quasi‐periodic emission. In this work we revisit heritage X‐ray data sets from the 1990s to 2015 and apply robust significance testing of emerging quasi‐periodicities, seeking to understand the robustness and regularity of previously reported quasi‐periodic emissions. Our analysis incorporates the use of the Rayleigh test as an alternative to Lomb‐Scargle analysis or Fast Fourier Transforms, where Rayleigh is particularly suited to a time‐tagged data set of sparse counts such as is common for jovian X‐ray data. Furthermore, the analysis techniques that we present (including Rayleigh testing and Monte Carlo simulation) can be applied to any time‐tagged data set. The code to conduct such analysis is released as supplementary information to accompany this paper. The five most significant (p value <0.01) quasi‐periods from Jupiter's northern auroral region have periods ranging from ~8.0 to 45.96 min, and the two most significant (p value <0.01) quasi‐periods from the south have periods of ~14.1 and ~34.9 min. The selection of a restrictive hot spot source region seems to be critical for detecting quasi‐periodic emission, suggesting that the site of pulsations may be spatially localized. Periods vary from one Jupiter rotation to the next in one long observation, and the north and south are shown to pulse independently in another conjugate observation. These results have important implications for understanding the driver of jovian X‐ray emission.

Lunar Cold Spots and Crater Production on the Moon

AbstractMapping of lunar nighttime surface temperatures has revealed anomalously low nighttime temperatures around recently formed impact craters on the Moon. The thermophysically distinct “cold spots” provide a way of identifying the most recently formed impact craters. Over 2,000 cold spot source craters were measured with diameters ranging from 43 m to 2.3 km. Comparison of the crater size‐frequency distribution with crater chronology models and crater counts of superposed craters on the ejecta of the largest cold spot craters constrains the retention time of the cold spots to no more than ~0.5–1.0 Myr with smaller cold spots possibly retained for only few hundred kyr. This would suggest a relatively rapid impact gardening rate with regolith overturn depths exceeding ~5 cm over this time scale. We observe a longitudinal heterogeneity in the cold spot distribution that reflects the Moon's synchronous rotation with a higher density of cold spots at the apex of motion. The magnitude of the asymmetry indicates the craters formed from a population of objects with low mean encounter velocities ~8.4 km/s. The larger cold spots (D > 800 m) do not follow this trend, and are concentrated on the trailing farside. This could result from a shorter retention time for larger cold spots on the leading hemisphere due to the greater number of smaller, superposed impacts. Alternatively, the abundance of large cold spots on the trailing farside resulted from a swarm of 100‐m‐scale impactors striking the Moon within the last ~0.5 Myr.

Light escape cones in local reference frames of Kerr\u2013de\xa0Sitter\xa0 black hole spacetimes and related black hole shadows

We construct the light escape cones of isotropic spot sources of radiation residing in special classes of reference frames in the Kerr–de Sitter (KdS) black hole spacetimes, namely in the fundamental class of ‘non-geodesic’ locally non-rotating reference frames (LNRFs), and two classes of ‘geodesic’ frames, the radial geodesic frames (RGFs), both falling and escaping, and the frames related to the circular geodesic orbits (CGFs). We compare the cones constructed in a given position for the LNRFs, RGFs, and CGFs. We have shown that the photons locally counter-rotating relative to LNRFs with positive impact parameter and negative covariant energy are confined to the ergosphere region. Finally, we demonstrate that the light escaping cones govern the shadows of black holes located in front of a radiating screen, as seen by the observers in the considered frames. For shadows related to distant static observers the LNRFs are relevant.

Monte Carlo simulations of elemental imaging using the neutron-associated particle technique.

The purpose of this study is to develop and employ a Monte Carlo (MC) simulation model of associated particle neutron elemental imaging (APNEI) in order to determine the three-dimensional (3D) imaging resolution of such a system by examining relevant physical and technological parameters and to thereby begin to explore the range of clinical applicability of APNEI to fields such as medical diagnostics, intervention, and etiological research. The presented APNEI model was defined in MCNP by a Gaussian-distributed and isotropic surface source emitting deuterium + deuterium (DD) neutrons, iron as the target element, nine iron-containing voxels (1 cm3 volume each) arranged in a 3-by-3 array as the interrogated volume of interest, and finally, by high-purity germanium (HPGe) gamma-ray detectors anterior and posterior to the 9-voxel array. The MCNP f8 pulse height tally was employed in conjunction with the PTRAC particle tracking function to not only determine the signal acquired from iron inelastic scatter gamma-rays but also to quantitate each of the nine target voxels' contribution to the overall iron signal - each detected iron inelastic scatter gamma-ray being traced to the source neutron which incited its emission. With the spatial, vector, and timing information of the series of events for each relevant neutron history as collected by PTRAC, realistic grayscale images of the distribution of iron concentration in the 9-voxel array were simulated in both the projective and depth dimensions. With an overall 225 ps timing resolution, 6.25 mm2 imaging plate pixels assumed to have well localized scintillation, and a DD neutron, Gaussian-distributed source spot with a diameter of 2 mm, projective and depth resolutions of < 1 cm and <3 cm are achievable, respectively, for iron-containing voxels on the order of 1,000 ppm Fe. The imaging resolution offered by APNEI of target elements such as iron lends itself to potential applications in disease diagnosis and treatment planning (high resolution) as well as to ordnance and contraband detection (low resolution). However, experimental study beyond simulation is required to optimize the layout and electronic configuration of APNEI system components - including realistic shielding and phantom materials - for background signal reduction in order to accurately determine the detection limits and spatial resolution of iron and other elements of interest on a case-by-case basis.

Tomography with extended sources: Theory, error estimates, and a reconstruction algorithm

Recently, an approach to tomography with extended anisotropic radiation sources has been introduced, which helps to overcome the challenges resulting from the low brilliance typical for x-ray laboratory sources. The method is based on the three-dimensional Radon transform (3DRT) which uses planar integrals instead of line integrals. By extending the source spot in one direction, more photons can contribute to image formation while the impact on the resolution is minor with the 3DRT approach. In this work we present a more comprehensive description of the method, derive quantitative error estimates for the extraction of these planar integrals measured with a finite source size, and validate the 3DRT scheme by analytical theory. We also demonstrate a simple and efficient reconstruction algorithm for 3D Radon data. Finally, we further substantiate the method with experimental results obtained at a microfocus x-ray source with an extremely anisotropic source spot.

Emittance Growth in the DARHT-II Linear Induction Accelerator

The Dual-Axis Radiographic Hydrotest (DARHT) facility uses bremsstrahlung radiation source spots produced by the focused electron beams from two linear induction accelerators (LIAs) to radiograph large hydrodynamic experiments driven by high explosives. Radiographic resolution is determined by the size of the source spot, and beam emittance is the ultimate limitation to spot size. Some of the possible causes for the emittance growth in the DARHT LIA have been investigated using particle-in-cell (PIC) codes, and are discussed in this article. The results suggest that the most likely source of emittance growth is a mismatch of the beam to the magnetic transport, which can cause beam halo.

Integrated optical Mach-Zehnder interferometer-based defect detection using a laser-generated ultrasonic guided wave.

The laser-based transmitter used in this Letter is composed of an integrated optical Mach-Zehnder interferometer, which was first used in fault diagnosis. With the help of the effective signal processing method and laser-based integrated optical Mach-Zehnder (IOMZ) system, the location of the defect in an aluminum plate can be successfully determined. Moreover, a comparison study is conducted to investigate the effectiveness of both the conventional laser spot source and the IOMZ interferometer-based laser source. The results indicate that the IOMZ interferometer-based method can be very useful to the nondestructive testing research field. The potential for industrial applications is also significant, especially for the health monitoring and integrity inspection of metal plates.

Pulsed flying spot with the logarithmic parabolas method for the estimation of in-plane thermal diffusivity fields on heterogeneous and anisotropic materials

A novel thermal non-destructive technique based on a Pulsed Flying Spot is presented here by considering in-plane logarithmic processing of the relaxing temperature field around the heat source spot. Recent progress made in optical control, lasers, and infrared cameras permits the acquisition of 2D temperature fields and localized thermal excitation on a small area instead of the entire recorded image. This study focuses on a new method based on spatial logarithm analysis of a temperature field to analyse and measure different parameters, such as the in-plane thermal diffusivity and localization of the spot. In this paper, this method is presented and the first results of heterogeneous anisotropic materials are depicted. The in-plane thermal diffusivity is estimated with an error lower than 4%, and the initial location of the heating spot is determined.

Prevalence of angular leaf spot disease and sources of resistance in common bean in eastern Democratic Republic of Congo

Angular leaf spot ( Pseudocercospora griseola Crous U, Brown) is one of the most important diseases hindering common bean ( Phaseolus vulgaris L.) production in the Great Lakes Region of Africa, including the Democratic Republic of Congo. The disease causes extreme yield losses, estimated at 384.2 tonnes per year, in Sub-Saharan Africa. Little is known about the distribution, severity and incidence of the disease and the effect of agronomic practices and environmental factors on the disease prevalence in the country to facilitate interventions. A field survey was conducted during two crop seasons, February to June and September to January, in two main beans growing zones of eastern DRC namely; sub-humid highland and sub-humid mid altitude at low latitudes, in South and North Kivu, respectively. Severity and incidence of angular leaf-spot and other occurring diseases were assessed on common bean plants in farmers’ fields. Angular leaf spot in these fields had an average severity index (PSI) of 49.9%. PSI was significantly different (P<0.05) between districts and seasons. Using multiple regression analysis, independent variables: growth stage, cropping system, districts and altitude were shown to have significant influence on the observed PSI (P<0.05) with R 2 = 96.2%. The highest severity (PSI=59.7%) was observed in Kabare district, and the lowest in Uvira district (PSI=39.5%). Screening of a set of 37 released common bean varieties in DRC using virulent Andean and Mesoamerican isolates identified four resistant bean varieties; ARA 4, COD MLV 059, MLV 224/94B, LSA 144 and Mexico 54. Some of these varieties possess useful traits, in addition to acceptable seed market class, and are hence recommended as suitable parents for ALS resistant variety development and promotion in ALS prone environments. Keywords: Phaseolus vulgaris , Pseudocercospora griseola , severity

Quantitative evaluation of surface crack depth with laser spot thermography

In this study, a numerical method based on finite element method (FEM) is developed to simulate the heat flow generated by laser spot source and investigate the relationship between crack size and temperature distribution. The feasibility of the simulation method is validated by experiments both in time and spatial domains. The simulation and experiment results also show that the crack depth can be described by two characteristic parameters. Furthermore, a quantitative retrieval method based on neural network is developed for the crack depth evaluation by using the parameters. By using the proposed method, crack depth can be determined only by analyzing measured surface temperature values.

Geochemical characteristics of soil radon and carbon dioxide within the Dead Sea Fault and Karasu Fault in the Amik Basin (Hatay), Turkey

The study area is close to the boundary of three tectonic plates (Anatolian, Arabian, and African plates) and is characterized by important tectonic lineaments, which consist mainly of the Dead Sea Fault (DSF), the Karasu Fault, and the East Anatolian Fault (EAF) systems. To understand the origin of soil gas emanation and its relationships with the tectonics of the Amik Basin (Hatay), a detailed soil gas sampling was systematically performed. Together with CO2 flux measurements, >220 soil gas samples were analyzed for Rn and CO2 concentrations. The distribution of soil Rn (kBq/m3), CO2 concentration (ppm), and CO2 flux (g/m2/day) in the area appears as a point source (spot) and/or diffuses (halo) anomalies along the buried faults/fractures due to crustal leaks. The results revealed that Rn and CO2 concentrations in the soil gas show anomalous values at the specific positions in the Amik Basin. The trace of these anomalous values is coincident with the N-S trending DSF. CO2 is believed to act as a carrier for Rn gas. Based on the Rn and CO2 concentrations of soil gases, at least three gas components are required to explain the observed variations. In addition to the atmospheric component, two other gas sources can be recognized. One is the deep crust component, which exhibits high Rn and CO2 concentrations, and is considered the best indicator for the surface location of fault/fracture zones in the region. The other component is a shallower gas source with high Rn concentration and low CO2 concentration. Moreover, He isotopic compositions of representative samples vary from 0.94 to 0.99 Ra, illustrating that most samples have a soil air component and may have mixed with some crustal component, without significant input of the mantle component. Based on the repeated measurements at a few sites, soil gas concentrations at the same site were observed to be higher in 2014 than in 2013, which may be associated with the activity of the DSF in 2013–2014. This suggests that soil gas variations at fault zone are closely related to the local crustal stress, and hence are suitable for monitoring fault activities.

Sapphire-Based Dammann Gratings for UV Beam Splitting

We report sapphire-based Dammann gratings (DGs) for ultraviolet (UV) beam (266 nm) splitting, which is fabricated via femtosecond laser direct writing assisted with subsequent wet etching. By applying 400-nm-wavelength laser processing followed by wet etching, smooth surface morphology, together with well-tailored geometry, was obtained. These DGs generated 2 × 2, 3 × 3, 4 × 4, and 5 × 5 spot sources in the fan-out as designed and exhibited diffraction efficiency of 59.26%, 39.53%, 44.68%, and 55.37%, respectively, comparable with theoretical values. Such sapphire-based DGs show great potential in UV beam shaping, UV beam splitting, and laser parallel microprocessing.