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نتیجه جستجو - Geometry

تعداد مقالات یافته شده: 74
ردیف عنوان نوع
1 Compensating over- and underexposure in optical target pose determination
Compensating over- and underexposure in optical target pose determination-2021
Optical coded targets allow to determine the relative pose of a camera, on a metric scale, from one image only. Furthermore, they are easily and efficiently detected, opening to a wide range of applications in robotics and computer vision. In this work we describe the effect of pixel saturation and non-ideal lens Point Spread Function, causing the apparent position of the corners and the edges of the target to change as a function of the camera exposure time. This effect, which we call exposure bias, is frequent in over- or underexposed images and introduces a systematic error in the estimated camera pose. We propose an algorithm that is able to estimate and correct for the exposure bias exploiting specific geometric features of a common target design based on concentric circles. Through rigorous laboratory experiments carried out in a highly controlled environment, we demonstrate that the proposed algorithm is seven times more precise and three times more accurate in the target distance estimation than the algorithms available in the literature.© 2021 Elsevier Ltd. All rights reserved.
Keywords: Optical target | Target orientation | Image processing algorithm | Geometry | Ellipse fitting | Computer vision | Overexposure | Exposure compensation | Resection
مقاله انگلیسی
2 Biometric recognition through 3D ultrasound hand geometry
تشخیص بیومتریک از طریق هندسه سونوگرافی سه بعدی دست-2021
Biometric recognition systems based on ultrasonic images have several advantages over other technologies, including the capability of capturing 3D images and detecting liveness. In this work, a recognition system based on hand geometry achieved through ultrasound images is proposed and experimentally evaluated. 3D images of human hand are acquired by performing parallel mechanical scans with a commercial ultrasound probe. Several 2D images are then extracted at increasing under-skin depths and, from each of them, up to 26 distances among key points of the hand are defined and computed to achieve a 2D template. A 3D template is then obtained by combining in several ways 2D templates of two or more images. A preliminary evaluation of the system is achieved by carrying out verification experiments on a home–made database. Results have shown a good recognition accuracy: the Equal Error Rate was 1.15% when a single 2D image is used and improved to 0.98% by using the 3D template. The possibility to upgrade the proposed system to a multimodal system, by extracting from the same volume other features like palmprint and hand veins, as well as possible improvements are finally discussed.
Keywords: Ultrasound imaging | Image processing | Biometry | Hand Geometry
مقاله انگلیسی
3 Opportunities and challenges of using biometrics for business: Developing a research agenda
فرصت ها و چالش های استفاده از بیومتریک برای تجارت: توسعه دستور کار تحقیقاتی-2021
Recently, biometric data generated by fingerprints, hand geometry, heart rate, voice patterns, facial character- istics and expressions, brain activity and body movement has increased in both volume and prominence. Surprisingly, academic business literature has remained relatively silent on the immense potential of biometric data, as well as on the various dangers that come with its collection and usage. This article sets out to (1) detail what biometric data entails and how it may be used, (2) describe opportunities associated with using biometric data in various business applications, (3) discuss challenges related to biometric data collection and usage, privacy and security, storage and safety, and potential for reduced inclusiveness and enhanced biases, and (4) outline related directions for future research.
Keywords: Biometrics | Technology | Ethics | Privacy | Security | AI | Bias
مقاله انگلیسی
4 Adaptive finite element eye model for the compensation of biometric influences on acoustic tonometry
مدل چشم اجزای محدود تطبیقی برای جبران تأثیرات بیومتریک بر تونومتری آکوستیک-2021
Background and objective: Glaucoma is currently a major cause for irreversible blindness worldwide. A risk factor and the only therapeutic control parameter is the intraocular pressure (IOP). The IOP is determined with tonometers, whose measurements are inevitably influenced by the geometry of the eye. Even though the corneal mechanics have been investigated to improve accuracy of Goldmann and air pulse tonometry, influences of geometric properties of the eye on an acoustic self-tonometer approach are still unresolved.
Methods: In order to understand and compensate for measurement deviations resulting from the geometric uniqueness of eyes, a finite element eye model is designed that considers all relevant eye components and is adjustable to all physiological shapes of the human eye.
Results: The general IOP-dependent behavior of the eye model is validated by laboratory measurements on porcine eyes. The difference between simulation and measurement is below 8 μm for IOP levels from 5 to 40 mmHg. The adaptive eye model is then used to quantify systematic uncertainty contributions of a variation of eye length and central corneal thickness based on input statistics of a clinical trial series. The adaptive eye model provides the required relation between biometric eye parameters and the corneal deflection amplitude, which here is the measured quantity to trace back to the IOP. Implementing the relations provided by the eye model in a Gaussian uncertainty propagation calculation now allows the quantification of the uncertainty contributions of the biometric parameters on the overall measurement uncertainty of the acoustic self-tonometer. As a result, a systematic uncertainty contribution resulting from deviations in eye length dominate stochastic deviations of the sensor equipment by a factor of 3.5.
Conclusion: As perspective, the proposed adaptive eye model provides the basis to compensate for systematic deviations of (but not only) the acoustic self-tonometer.
Keywords: Corneal vibration | Transient simulation | FEM | Eye model | Intraocular pressure | Glaucoma
مقاله انگلیسی
5 Analyzing the effects of machining parameters on surface roughness of machined surfaces using vision system
تجزیه و تحلیل اثرات پارامترهای ماشینکاری بر زبری سطح سطوح ماشینکاری با استفاده از سیستم بینایی-2021
Surface roughness measurement of machined components helps in predicting the success or failure of component when it is put into service. Surface roughness measurement is also used to judge capability of manufacturing process. Surface roughness evaluation is also used for monitoring the condition of cutting tool or machine tool. Any change in process parameter or condition of the cutting tool results in changes in surface geometry and texture. Usually, the factors affecting the machining capability are its own inherent properties such as, feed, speed, depth of cut, tools, coolant flow rate etc. Relationship between stylus measured roughness and vision surface roughness (Ra) has been studied. As for as the knowledge of authors no research work has been reported about determining the effects of cutting parameters on surface roughness of milled components. In this context, the present research works assumes special significance. An attempt has been made in the current research work to explore the effect of cutting parameters on surface roughness of milled surfaces using vision system.© 2021 Elsevier Ltd. All rights reserved.
Keywords: Surface roughness | Vision system | Machine tool | Cutting tool | Machining parameters
مقاله انگلیسی
6 A computational-geometry-based 3-dimensional guidance law tocontrol impact time and angle
قانون راهنمایی 3 بعدی مبتنی بر محاسباتی-هندسه ، زمان و زاویه و تاثیر کنترل -2020
In this paper, a new guidance law is proposed based on computational geometry with impact time and angle constraints against a stationary target in three dimensions. The law is based on the principle of following a specified trajectory toward the target, and this trajectory is composed of a log-aesthetic space curve segment and a collision line segment. The collision line formulates a direction identical to the desired impact angle, which leads to the satisfaction of the impact angle constraint. The log-aesthetic space curve is used to drive the missile from the initial velocity vector to the collision line. The impact time is controlled by adjusting the trajectory length, which is realized by tuning the end point position of the curve segment along the collision line. Moreover, the position range of the end point and the maximum curvature of the trajectory are considered to ensure that the trajectory is achievable and flyable. A numerical iterative method is used to determine the end point position and curve parameters of the required trajectory. Numerical simulations are demonstrated to illustrate the performance of the proposed method in simultaneous attack scenarios.
Keywords: Three-dimensional guidance | Computational geometry | Impact angle control | Impact time control
مقاله انگلیسی
7 Determination of the shear traction-separation law of adhesive layers using the end-notched flexure specimen
تعیین قانون جداسازی کشش و برشی لایه های چسبنده با استفاده از نمونه خمشی انتهایی-2020
Cohesive zone modelling is increasingly applied to predict the strength of structural adhesive joints. A method is here proposed to determine the bondline shear traction-separation law needed for cohesive zone models. The method combines an effective crack length approach derived from a beam model and an existing J-integral analysis of the end-notched flexure specimen. The resulting work done by the tractions versus separation curves can be easily processed with direct or mixed direct-inverse approaches. Application to some published experimental results demonstrates the potential of the method while highlighting the importance of adherend material and specimen geometry selection.
Keywords: Adhesive joints | Toughness testing | End-Notched Flexure | Beam model | Cohesive zone modelling
مقاله انگلیسی
8 A Hermite WENO scheme with artificial linear weights for hyperbolic conservation laws
یک طرح هرمیت WENO با وزن خطی مصنوعی برای قوانین حفاظت از hyperbolic-2020
In this paper, a fifth-order Hermite weighted essentially non-oscillatory (HWENO) scheme with artificial linear weights is proposed for one and two dimensional hyperbolic conservation laws, where the zeroth-order and the first-order moments are used in the spatial reconstruction. We construct the HWENO methodology using a nonlinear convex combination of a high degree polynomial with several low degree polynomials, and the associated linear weights can be any artificial positive numbers with only requirement that their summation equals one. The one advantage of the HWENO scheme is its simplicity and easy extension to multi-dimension in engineering applications for we can use any artificial linear weights which are independent on geometry of mesh. The another advantage is its higher order numerical accuracy using less candidate stencils for two dimensional problems. In addition, the HWENO scheme still keeps the compactness as only immediate neighbor information is needed in the reconstruction and has high efficiency for directly using linear approximation in the smooth regions. In order to avoid nonphysical oscillations nearby strong shocks or contact discontinuities, we adopt the thought of limiter for discontinuous Galerkin method to control the spurious oscillations. Some benchmark numerical tests are performed to demonstrate the capability of the proposed scheme.
Keywords: Hermite WENO scheme | Hyperbolic conservation laws | Unequal size spatial stencil | Hybrid | Discontinuous Galerkin method
مقاله انگلیسی
9 Design optimization of a cross-flow He-Xe recuperator through second law analysis
بهينه سازي طراحي عبور متقابل جریان He-Xe از طريق تحليل قانون دوم-2020
Nuclear power conversion in space has been approached by various means since the first space missions, with the advent of concepts such as thermoelectric, thermionic and thermodynamic conversion. Nowadays, thermal cycles are under greater focus for being capable of providing higher conversion efficiencies. In this context, one of the main concerns of engineers is the trade-off between power and mass. Therefore, this work aims the optimization of a recuperator used in a regenerative closed Brayton cycle applied for power conversion in the project of a small-scale nuclear reactor. The recuperator consists of a cross-flow, shell-and-tube heat exchanger with a matrix of tubes distributed in a staggered configuration. In this work, the number of tubes and the mass flow rate are varied. The number of tubes distributed axially is fixed as 4, whereas the quantity around the axis can be 5, 7, 9, 12 and 16 tubes. The working fluid considered in this study is a mixture of noble gases He-Xe with a molecular weight of 40 g/mol, whereas Inconel alloy 617 is applied as the recuperator material. The optimization procedure was based on the entropy generation minimization and the heat exchanger effectiveness, using the Computational Fluid Dynamics (CFD) technique to obtain the flow field. Optimum mass flow rates are obtained for all the geometries at the points of minimum entropy generation number, around which lie the ranges of tested mass flow rates. The ratio between the entropy generation number and effectiveness associated with the optimum mass flow rate is considered a performance evaluation criterion, and the dependence of this parameter with exchanger mass is assessed in order to select the most suitable geometry for the studied application. This analysis leads to the optimum design point at the geometry of 9 tubes around the recuperator axis, yielding a lost available work of 929.76 W for an ambient temperature of 298 K.
Keywords: Optimization | Recuperator | CFD | Second law | Entropy
مقاله انگلیسی
10 Semi-automated generation of parametric BIM for steel structures based on terrestrial laser scanning data
تولید نیمه خودکار BIM پارامتری برای سازه های فلزی بر اساس داده های اسکن لیزری زمینی-2020
As-built building information models (BIMs) are increasingly needed for construction project handover and facility management. To create as-built BIMs, laser scanning technology has gained popularity in the recent decades due to its high measurement accuracy and high measurement speed. However, most existing methods for creating as-built BIMs from laser scanning data involve plenty of manual work, thus becoming labor intensive and time consuming. To address the problems, this study presents a semi-automated approach that can obtain required parameters to create as-built BIMs for steel structures with complex connections from terrestrial laser scanning data. An algorithm based on principal component analysis (PCA) and cross-section fitting techniques is developed to retrieve the position and direction of each circular structural component from scanning data. An image-assisted edge point extraction algorithm is developed to effectively extract the boundaries of planar structural components. Normal-based region growing algorithm and random sample consensus (RANSAC) algorithm are adopted to model the connections between structural components. The proposed approach was validated on a bridge-like steel structure with four different types of structural components. The extracted asbuilt geometry was compared with the as-designed geometry to validate the accuracy of the proposed approach. The results showed that the proposed approach could efficiently and accurately extract the geometry information and generate parametric BIMs of steel structures.
Keywords: Building information model (BIM) | Terrestrial laser scanning | As-built geometric modeling
مقاله انگلیسی
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