Line Source Research Articles

Stationary prospective cardiac gated computed tomography—dynamic study in phantoms and in vivo

Objective. This study explores the feasibility of a stationary gantry cardiac gated computed tomography (CT) with carbon nanotube (CNT) linear x-ray source arrays. Approach. We developed a stationary gantry CT system utilizing multipixel CNT x-ray sources. Given the advantages of straightforward x-ray pulse control with these sources, we investigated the potential for gated prospective imaging. We implemented prospective respiratory and cardiac gating control and evaluated the system through dynamic phantom imaging studies followed by imaging of a porcine model. Main Results. The findings revealed minimal anatomical motion artifacts in the heart and lungs, confirming successful physiologic gated acquisition in stationary gantry cardiac CT. This indicates the potential of this imaging approach for reducing artifacts and improving image quality. Significance. This study demonstrates the feasibility of prospective physiological gating with CNT x-ray sources in a stationary gantry setup for cardiac imaging. This approach could potentially alleviate the need for beta blocker administration during cardiac CT scans, thereby increasing the flexibility of the imaging system and enabling the imaging of a wider variety of patient cardiac conditions.

Impact of various heat sources on the transient heat transfer rate in a 3D cylinder consisting of parts with different thermal conductivity coefficients

Numerical analysis of time-dependent conductive heat transfer in three-dimensional solid bodies with a heat source is important in their use in various industries. In this article, an attempt has been made to investigate this issue for a cylinder consisting of four equal pieces with different thermal conductivity coefficients and heat sources, and conclusions have been drawn. The geometry of the cylinder consists of two lower (first) and upper (second) layers. In the lower layer of two solid bodies, one is a piece of rubber with a thermal conductivity coefficient of K1=0.16 w/m○k and the other is a piece of walnut wood with a thermal conductivity coefficient of K2=0.077 w/m○k and two solid objects are used in the upper layer. One is a piece of polyurethane with a thermal conductivity coefficient of K3=0.02 w/m○k and the other is a piece of cork with a thermal conductivity coefficient of K4=0.04 w/m○k. There are four heat source mechanisms: constant value, linear, quadratic, and sinusoidal or periodic heat source with a certain frequency. All the surfaces of the cylinder walls in the time interval 0 ≤ t ≤ 10 s10, T=0 are assumed. The obtained results show that the temperature distribution when the value of the heat source is constant affects a larger area, and the highest increase in temperature in the direction of the z-axis belongs to the constant, quadratic, sinusoidal and linear heat source, respectively.

Miniaturized spectroscopy system based on a semiconductor nanofilm

Abstract Spectroscopy plays a pivotal role in various applications for industrial and commercial analysis. Conventional spectroscopy instruments include various discrete optical components like light sources, monochromators and detectors. These components are mechanically intricate and require space for the mechanisms that adjust and calibrate them, which increases the instrument’s footprint and make them less adjustable for portable applications. This drawback initiated the increase in the demand for miniatured spectral detection systems. Here, we present a low-cost ultra-compact miniaturized spectral detection system, which integrates both linear variable light sources, sample chambers and detectors within a centimetre-scale chip. The linear variable light generation across wavelengths ranging from 480 nm to 600 nm is achieved by stimulating different regions of the ZnCdSeS bandgap-graded semiconductor nanofilm with ultraviolet light. We demonstrate the capability of the system with precise identification of liquids. Our device overcomes the typical miniaturization limits imposed by discrete optical components, and long light paths in conventional spectroscopy instruments and opens up numerous potential applications across various fields due to its portability, ease of use, and lower cost.

Advances in optical coating uniformity of interference filters

We propose a method to obtain uniform multilayer coatings using vacuum assemblies with a linear ion source to manufacture narrow-band interference filters essential in astrophysical research for space object imaging in important spectral lines, and to provide multi-channel fiber-optic transmission of information. Interference filters and other optical systems, for example, high-reflective mirrors, steep-front beam splitters contain up to hundreds of film layers deposited onto a substrate. During the coating deposition, film thickness on the substrate must be strictly withstood and be uniform throughout the entire surface. This can be achieved by placing the linear source and target on the same platform and by conducting a test target sputtering on a fixed substrate. There is an inflection line on the coating thickness distribution on the substrate. By moving the platform, the inflection line midpoint is aligned with the center of the rotating working substrate, and in this position, the substrate is coated to a specified thickness, which is monitored during the deposition process.

Vertical line time domain green function and its applications in numerical simulation of ship seakeeping performance

In present study, a vertical line source time domain Green function is proposed and the subsequent numerical evaluation methods are described in detail. For which, Taylor expansion and Chebyshev approximation algorithms are originally extended from point source to line source for small parameters, as well as asymptotic expansions are extended for large parameters. Meanwhile, polynomials are originally proposed to replace the asymptotic expansions to improve the computational efficiency. The accuracy and stability of the proposed method are validated through several cases and good agreement can be obtained.Furthermore, a hybrid Green function method based on the vertical line source Green function and Rankine source is developed for time domain simulation of seakeeping performances of ships. With respect to the hybrid method, the flow domain is divided into inner part and outer part by an artificial control surface. The first-order Taylor Expansion Boundary Element Method (TEBEM) based on the Rankine panel distribution is applied in the inner part, while three-dimensional panel method based on the vertical line source Green function distribution is adopted in the outer part. Under this circumstance, motions of the single-ship (Slender Wigley and Blunt Wigley) and two-ship (two side-by-side ships) in head waves are numerically investigated. The numerical results agree well with the experimental data, which proved the feasibility and the accuracy of present hybrid Green function method for motion prediction of both single-ship and two-ship.

Asymptotic expansion method with respect to a small parameter for fractional differential equations with Riemann–Liouville derivate

In this paper, we proposed an asymptotic approach with respect to a small parameter for fractional differential equations, with the small parameter linked to the fractional order derivative. This approach allows the splitting of the field variable and consequently the Riemann–Liouville Integral as the sum of two contributions. One describes the unperturbed state and the other describes the behavior of the model in the perturbed state due to the presence of the fractional derivative. This approach allows mapping time-fractional differential equations into a system of two coupled partial differential equations with integer order. By solving these partial differential equations we are able to obtain solutions of the assigned fractional differential equations. To obtain solutions we determine the approximate Lie symmetries through which the system of two coupled partial differential equations is reduced to a system of two coupled ordinary differential equations. As an application, we consider the time fractional diffusion–reaction equation with a linear source term; we test the proposed procedure by comparing the profiles of the obtained approximate solutions with solutions found in the fractional context for values of the fractional parameter tending to the integer value.

Time-modulated planar frequency diverse array for multi-target detection

The frequency diverse array (FDA) is a very interesting technique in wireless communications. Many research papers are introduced in this field. A lot of them is concerned with linear point sources array. In this paper, a design of a time-modulated planar frequency diverse array architecture is proposed for tracking single or multi-target for the first time. The time-modulation array (TMA) and FDA are combined for detecting single and multi-target. The effectiveness of this combined scheme is demonstrated through simulation results that compared with a point source case to show its superior performance. Authors introduce planar FDA array instead of linear FDA array and realize the planar array using cylindrical dielectric resonator antenna array (CDRA). A planar array consists of 8 × 8 CDRA is used to enable the detection of single target/multi-target. The operating frequency of the antenna is set at 10 GHz, aligning with its applications in the FDA radar. The radiation characteristics of the CDRA antenna element are introduced. High maximum gain of 6 dBi is achieved with a remarkably high efficiency. A set of representative results is reported and analyzed to assess the effectiveness of the proposed approach.

Geomorphological and morphometric characterization of subglacial channels on Devon Island, Nunavut, Canada

Subglacial channels are morphologically and morphometrically distinct in comparison to fluvial channels, yet their identification from remote sensing data is still problematic. To contribute to the current set of criteria used to identify such channels, we performed a detailed analysis of two subglacial channel networks on Devon Island, Nunavut, Canada. In planform, these channels are isolated, finger-like networks that drain into a main stem and have distinct cross-sectional and longitudinal profiles. Cross-sections are flat-bottomed with steep walls and longitudinal profiles are convex and exhibit undulations, typical of pressurized water flow (i.e., subglacial flow). To facilitate remote sensing identification, we interrogated how well-known scaling relationships capturing hydraulics and mass balance dynamics of fluvial systems differ in subglacial channels. Scaling relationships typically used to discern connections between discharge and channel and catchment size in fluvial systems were applied to both networks, yielding trends distinct from the fluvial literature. We suggest that the weakly correlated relationship we found between channel discharge and the size of the drainage area indicates a discrete point or line source of water, such as a moulin or crevasse.

Source characterization of a ducted source using acoustic free velocity

A common method to characterize linear time invariant ducted acoustic sources is the electro-acoustic analogy. The sources are typically defined by their internal source strength and source impedance. Various methods have emerged to determine the source characteristics, broadly categorized into direct and indirect methods. Direct methods involve using a secondary source with significantly higher amplitude to measure source impedance but cannot determine source strength. Indirect methods vary acoustic loads to obtain both source strength and source impedance, accuracy depends on appropriate load combinations. In this research, we propose an inverse method to determine the acoustic source strength from the measured acoustic transfer function and the operational acoustic pressure. This approach yields what we term as the "acoustic free velocity," corresponding to a plane monopole source that characterizes the original sound source. Subsequently, the source impedance is obtained using the acoustic free velocity in conjunction with the load impedance and acoustic pressure in the acoustic circuit. The method is demonstrated using a compressor driver source attached to a 1 3/8" impedance tube. Validation of the measured source strength and source impedance is conducted using a two-load method. Additionally, prediction of muffler insertion loss shows a good correlation with experimental measurements, affirming the efficacy of the proposed methodology.

Dynamics of a linear source epidemic system with diffusion and media impact

Dynamics of a linear source epidemic system with diffusion and media impact

Surface crack detection on selective laser melting printed Inconel 718 using a laser generated ultrasound technique and phase space reconstruction

Abstract In the field of metallic additive manufacturing, Selective Laser Melting (SLM) has become a predominant technology due to its advantages of short production cycles, high precision, and low cost. It is frequently employed in the production of complex parts. This paper proposes the use of a scanning laser line source, in conjunction with the singular value decomposition method, to reconstruct phase space and identify surface cracks in SLM specimens. The scanning laser line source addresses the limitations of a single line source, which is often unable to accurately detect tiny cracks. By comparing experimental and simulation data, the results demonstrate that the scanning laser line source can effectively compensate for some of the detection deficiencies of a single line source.

Multiscale Topology Optimization Design and Additive Manufacturing of Thermal Expander Metadevices

Thermal expander metadevices can yield a large uniform temperature field powered by a linear heat source. Previous design of thermal expander metadevices can be regarded as a combination of achieved thermal cloaks and their background materials. However, these thermal-cloak-inspired expander metadevices have an inherent flaw, i.e., their thermal functionality will be lost when the background material is changed, thus limiting their practical applications. To solve this problem, the multiscale topology optimization (MTO) method is employed to design thermal expander metadevices that can maintain their expander functionality under different background materials. In MTO, transformation thermotic technology is used to determine the anisotropic thermal conductivities inside a thermal expander metadevice and topology optimization is performed to generate the topological configuration of each microstructure with the target effective thermal conductivity. Subsequently, the thermal functionalities of thermal double and triple expander metadevices with different background materials are numerically verified via simulations. Finally, the thermal double expander metadevice is fabricated via additive manufacturing and experimentally tested for its thermal functionality. The findings of this study address the challenge of designing thermal expander metadevices with background material-independent functionality.

Suitability of using carbon dioxide as a tracer gas for studying vehicle emission dispersion in a real street canyon

High-rise buildings form deep urban street canyons and restrict the dispersion of vehicle emissions, posing severe health risks to the public by aggravating roadside air quality. Field measurements are important for understanding the dispersion process of tailpipe emissions in street canyons, while a major challenge is the lack of a suitable tracer gas. Carbon dioxide (CO2), which is safe to the public and inexpensive to obtain, can be reliably measured by existing gas analysers. This study investigated the suitability of using CO2 as a tracer gas for characterising vehicle emission dispersion in a real-world street canyon. The tracer gas was released via a line or point source, whose dispersion was characterised by a sensors network comprising low-cost air quality sensors. The results showed that the CO2 contained in the exhaust gas of a test vehicle itself had unmeasurable effect at roadsides. Both the line and point sources produced obvious CO2 level elevations at approximately 30 s after the test vehicle passed by. In addition, for both line and point sources, the CO2 elevations were much more distinct at the roadside next to tailpipe exit than the opposite side, and were higher at 0.8 m than 1.6 m above the ground. The present study demonstrated that using CO2 as a tracer gas is feasible for investigating vehicle emission dispersion in real-world street canyons. Future studies are needed to improve the gas release rate of the developed tracer gas systems for more reliable measurements and larger street canyons.

Transfer learning-based drive-by monitoring of railway tracks

Track quality significantly impacts passenger comfort and safety. The maintenance of track quality involves routine monitoring of track geometry and track component defects. In a drive-by monitoring framework, vibration data are collected from operational trains providing an effective and low-cost track monitoring system. This framework enables each train to inspect multiple lines without the need to install and maintain sensors on each line. In conventional data-driven frameworks that utilize machine learning or statistical models, geometrical defects diagnosis model is often constructed using supervised learning. Supervised learning requires response data and corresponding damage states (i.e., labels) for each railway line to learn the line-specific damage diagnosis model. However, labelled data are frequently unavailable for many lines in practical situations, making it challenging to construct a damage diagnosis model. Furthermore, using data directly from source line to construct a damage diagnosis model for the target line can lead to inaccurate results. To this end, in this paper, a novel drive-by monitoring framework is proposed based on Transfer Learning (TL) concept. This approach transfers the geometrical defects diagnosis model learned from one line to a new line. Firstly, condition-sensitive time domain features are extracted from the raw data. Then, a deep learning model based on the long short-term memory (LSTM) network is trained on a dataset from one line (source domain) and fine-tuned for a new dataset using a small number of samples from another line (target domain). The effectiveness of this framework is compared through the classification performance using real-world monitoring datasets collected from two different lines of the France railways network. The results demonstrate up to a 22% increase in defect detection accuracy compared to the basic method.

Flow-field characteristics of the thermal plume above an elliptical high-temperature heat source surface

The thermal plume formed by the high-temperature elliptical heat source surface during the smelting process is often captured and removed by the local exhaust system. Accurately mastering the flow-field characteristics of such high-temperature elliptical heat plumes is helpful for efficient design of local exhaust systems. In this paper, the effects of the ratio of long and short axes (5/4 ≤ ξ ≤ 5/1) and the intensity of heat source (80 ≤ F ≤ 160 W) on the axial and radial velocity distribution of thermal plume in an elliptical heat source are investigated by numerical simulation combined with experimental validation. The results show that in the range of ξ ≤ 5/1, the axial dimensionless velocity distribution of the elliptical plume field and the spreading range of the plume field are mainly affected by ξ instead of F. For 5/4 ≤ ξ ≤ 5/1, the maximum axial velocity Um appears at 1.7 to 2.7 times Z/L (plume height to heat source long axis ratio). For ξ ≤ 5/2, the height at which the cross-sectional velocity field transitions to a circular distribution aligns with the height of Um. It is found that the plume velocity field is characterized by applying the point source model for ξ ≤ 5/3, and vice versa for the linear source model. The plume flow rate formulation obtained by modifying the linear source model for ξ > 5/3 has a better predictive ability in the Z/L ≤ 5 region. This study provides a reference for the design of ventilation systems for elliptical surface heat sources.

Shale Oil Shut-In and Flowback Mechanism and Optimization Strategy

Abstract Shut-in and flowback are critical stages following hydraulic fracturing in shale oil wells. Researching the distribution of reservoir pressure and fluid flow mechanism during shut-in and flowback is important for optimizing these procedures, thereby enhancing well productivity. Therefore, based on the flow mechanism of shale oil, this article establishes a flow equation considering imbibition and seepage, using linear source superposition equivalent to the pressure distribution generated by hydraulic fracturing as the initial condition. The PEBI (Perpendicular BIsection) grid is used to divide the grid for multistage fractured horizontal wells. The simulation results reveal that large-volume fracturing leads to the formation of a high-pressure zone around the wellbore, significantly surpassing the original reservoir pressure, termed as the high-energy band. This high-energy band is demarcated from the original reservoir pressure by the pressure boundary line (PBL). During production, a double-pressure funnel (DPF) manifests within the reservoir, generating a region with the utmost pressure at a specific position within the high-energy band, known as the pressure peak line. Oil located beyond the pressure peak line is unable to flow toward the wellbore. According to the DPF theory of shale oil, fracturing technology should be adopted to form long straight fractures as far as possible whenever feasible to cross the high-energy band. The shale oil optimal duration for shut-in is contingent upon the movement rate of the pressure boundary and the shale imbibition curve.

Annealing of bismuth telluride-based thick films by laser irradiation

Interest towards fabrication and post-processing of thermoelectric micro-sized devices has increased in recent years. The coupling of inexpensive deposition technologies and fast laser treatments on “as-deposited” films is an attractive solution for industrial scalability. In this work, we propose an approach never reported before in literature: the utilization of a ns-pulsed active fibre laser to directly densify p-type bismuth telluride-based thick films deposited on silicon. A feasibility study was conducted on the material to determine optimal laser parameters: the treated products were characterized, and it was concluded that a value of laser fluence as low as 4.5 mJ cm−2 is sufficient for densification. The material resulted cracked after the laser treatment, and it was demonstrated by SEM and profilometric analyses that shrinking occurs and sintering necks are formed; further, the arising of second phases after annealing was excluded by means of XRD analysis. Envisioning an industrial large area process with linear diode arrays source, a prediction of the laser power requirements to irradiate 1 mm2 films in selected conditions is presented. More extensive studies will be performed to determine a narrower parameters window and determine a relationship between the film thickness and laser parameters for future applications to as-deposited films.

Experimental and Numerical Studies of Modified Polyurethane Diffusion Behavior in Vertical Cracks Based on Line Source Grouting

Experimental and Numerical Studies of Modified Polyurethane Diffusion Behavior in Vertical Cracks Based on Line Source Grouting

On the Accuracy of Transport Spatial Discretization Methods for Diffusive Regimes

An infinite-medium analysis is performed for neutron transport spatial discretization methods in planar geometry. Angular flux solutions of the spatially continuous transport equation, which are driven by a linear (or quadratic) source, are shown to vary linearly (or quadratically) in space and angle; these are used to assess whether the discretized transport equations preserve certain cell-averaged and edge quantities. Each of the continuous angular flux solutions has a scalar flux that satisfies the standard diffusion equation; our analysis predicts whether the transport discretizations yield an accurate diffusion coefficient and (diffusion) spatial differencing scheme. The linear moment–based discretization methods under consideration, which are found to preserve certain features of the linear (or quadratic) infinite-medium angular flux solutions, are the familiar linear discontinuous (LD), lumped linear discontinuous (LLD), and linear characteristic (LC) schemes. The step characteristic scheme, which yields an unphysically large diffusion coefficient, is revisited and shown to possess, for diffusive problems, a solution error that would occur if an unphysical anisotropic scattering term had been included in the starting discretized S N transport equations. The numerical results verify the theoretical predictions and demonstrate the accuracy of the LD, LLD, and LC schemes in highly scattering problems that are optically thick. Our numerical results also illustrate the impact of inaccuracies in the diffusion coefficient on the numerical solutions of eigenvalue problems. The analysis in this paper has practical implications in the choice of spatial schemes used to solve realistic eigenvalue problems.

A Binocular Color Line-Scanning Stereo Vision System for Heavy Rail Surface Detection and Correction Method of Motion Distortion.

Thanks to the line-scanning camera, the measurement method based on line-scanning stereo vision has high optical accuracy, data transmission efficiency, and a wide field of vision. It is more suitable for continuous operation and high-speed transmission of industrial product detection sites. However, the one-dimensional imaging characteristics of the line-scanning camera cause motion distortion during image data acquisition, which directly affects the accuracy of detection. Effectively reducing the influence of motion distortion is the primary problem to ensure detection accuracy. To obtain the two-dimensional color image and three-dimensional contour data of the heavy rail surface at the same time, a binocular color line-scanning stereo vision system is designed to collect the heavy rail surface data combined with the bright field illumination of the symmetrical linear light source. Aiming at the image motion distortion caused by system installation error and collaborative acquisition frame rate mismatch, this paper uses the checkerboard target and two-step cubature Kalman filter algorithm to solve the nonlinear parameters in the motion distortion model, estimate the real motion, and correct the image information. The experiments show that the accuracy of the data contained in the image is improved by 57.3% after correction.