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We present an approximation method of circular arcs using linear-normal (LN) Bézier curves of even degree, four and higher. Our method achieves Gm continuity for endpoint interpolation of a circular arc by a LN Bézier curve of degree 2m , for m=2,3. We also present the exact Hausdorff distance between the circular arc and the approximating LN Bézier curve. We show that the LN curve has an approximation order of 2m+2, for m=2,3. Our approximation method can be applied to offset approximation, so obtaining a rational Bézier curve as an offset approximant. We derive an algorithm for offset approximation based on the LN circle approximation and illustrate our method with some numerical examples. 相似文献
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运用物理光学分析方法,对使用7单元的扇形喇叭一维阵列和角锥喇叭或圆锥喇叭三角形阵列喇叭束作为单偏置抛物面天线的馈源,空间合成高功率微波进行了比较研究,数值分析表明在阵元输入功率、口面最大场强、天线口径、净空间及天线边缘照度相同,且阵列馈源具有准轴对称主瓣条件下,扇形喇叭构成的一维阵列馈源与单偏置抛物面组成的天线系统的方向性系数和溢出效率优于采用角锥喇叭三角形阵列馈源或圆锥喇叭三角形阵列馈源的天线系统。若将喇叭束直接作为辐射天线使用,由于圆锥喇叭三角形阵列方向性系数对阵元间相位波动的稳定性较好,而更具优势。 相似文献
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Two-level injection-locked opto-electronic oscillator is proposed for low phase noise. Dielectric resonator oscillator (DRO) is used as the first injection source, injection locking a long-fiber loop based opto-electronic oscillator, then its output is injection locking another long-fiber opto-electronic oscillator for getting a lower-phase noise output carrier. After the first injection, the single side band (SSB) phase noise at 10 kHz offset frequency decreases from −123 dBc/Hz to −135 dBc/Hz, then through the second injection the SSB phase noise drops down to −146 dBc/Hz. 相似文献
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Actual melt temperatures are rarely measured directly when conducting rheological characterisations of materials in non-ambient
conditions despite the potentially large influence temperature may have on the rheological data. For rheometers that use only
a temperature-regulated lower plate, it is likely that the set point and true melt temperatures differ, an effect that becomes
significant when characterising melts or suspensions close to phase-change events like crystallisation. This work investigates
the magnitude of these effects for a controlled-stress rheometer featuring a temperature-controlled lower plate. The lower
plate was fitted with a serrated cover disc that was found to exacerbate temperature deviations from the desired set point.
Steady-state radial and vertical temperature profiles within the sample were measured and compared with the predictions of
a finite element analysis model. The deviations between set point and measured temperatures were successfully predicted by
the simulation for two typical gap heights for a thermoplastic, ceramic paste. The non-ideal heat transfer characteristics
were also investigated numerically for a representative polymer system that demonstrated the increased deviations from ideal
values for lower thermal conductivity materials.
相似文献
D. Ian WilsonEmail: |
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Circular meshes are quadrilateral meshes all of whose faces possess a circumcircle, whereas conical meshes are planar quadrilateral
meshes where the faces which meet in a vertex are tangent to a right circular cone. Both are amenable to geometric modeling
– recently surface approximation and subdivision-like refinement processes have been studied. In this paper we extend the
original defining property of conical meshes, namely the existence of face/face offset meshes at constant distance, to circular
meshes. We study the close relation between circular and conical meshes, their vertex/vertex and face/face offsets, as well
as their discrete normals and focal meshes. In particular we show how to construct a two-parameter family of circular (resp.,
conical) meshes from a given conical (resp., circular) mesh. We further discuss meshes which have both properties and their
relation to discrete surfaces of negative Gaussian curvature. The offset properties of special quadrilateral meshes and the
three-dimensional support structures derived from them are highly relevant for computational architectural design of freeform
structures. Another aspect important for design is that both circular and conical meshes provide a discretization of the principal
curvature lines of a smooth surface, so the mesh polylines represent principal features of the surface described by the mesh.
相似文献
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A method was developed for measuring the residual solvent content in a dried offset print. The method is based on hexane extraction. The presence of additives and resins in the printing inks necessitated purification of the extract on an aluminum oxide column. In the study concerning the effect of the heatset web offset drying process on print quality, a distinct correlation was found between the residual solvent content of the print and the drying parameters. 相似文献
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We demonstrate the potential of Raman spectroscopy to detect cocaine concealed inside transparent glass bottles containing alcoholic beverages. A clear Raman signature of cocaine with good signal-to-noise was obtained from a ∼300 g solution of adulterated cocaine (purity 75%) in a 0.7 L authentic brown bottle of rum with 1 s acquisition time. The detection limit was estimated to be of the order of 9 g of pure cocaine per 0.7 L (∼0.04 moles L−1) with 1 s acquisition time. The technique holds great promise for the fast, non-invasive, detection of concealed illicit compounds inside beverages using portable Raman instruments, thus permitting drug trafficking to be combated more effectively. 相似文献
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Atiyeh Bayani Karthikeyan Rajagopal Abdul Jalil M. Khalaf Sajad Jafari G.D. Leutcho J. Kengne 《Physics letters. A》2019,383(13):1450-1456
Analyzing chaotic systems with coexisting and hidden attractors has been receiving much attention recently. In this article, we analyze a four dimensional chaotic system which has a plane as the equilibrium points. Also this system is of the group of systems that have coexisting attractors. First, the system is introduced and then stability analysis, bifurcation diagram and Largest Lyapunov exponent of this system are presented as methods to analyze the multistability of the system. These methods reveal that in some ranges of the parameter, this chaotic system has three different types of coexisting attractors, chaotic, stable node and limit cycle. Some interesting dynamics properties such as reversals of period doubling bifurcation and offset boosting are also presented. 相似文献