Extremum Lines Research Articles

Experimental study on the phase inhomogeneity and separability in supercritical state of acetone fuel

Sufficient understanding of the supercritical state is important for exploring supercritical jet spray in thermodynamic cycle power machinery. However, in conventional studies, the phase division of supercritical state and supercritical jet spray is simple and rough, and whether the pseudo-boiling (or widom) line exists widely in various fluids, especially fossil fuels, is still not proved by experiments. In this paper, the phase inhomogeneity and separability in the supercritical state of fossil fuels are studied by using high-speed Mie scattering and UV-LAS (ultraviolet–visible laser absorption/scattering) optical diagnostic techniques. Acetone is selected as the single representative component of fossil fuels. The results show that acetone is inhomogeneous in the supercritical state at fuel temperature Tf<1.13Tc and fuel pressure Pf<1.74Pc, where Tc and Pc are the critical temperature and pressure, and can be further divided into liquid-like phase and gas-like phase, which is similar to the properties of inert fluids and simple fluids reported in previous literatures. The transition region (measured at interval of pressure 0.2 MPa) between the liquid-like phase and gas-like phase contains thermodynamic extremum lines such as constant pressure specific heat, volume expansion coefficient, and isothermal compression rate, which supports the view that the widom (or pseudo-boiling) line is used as the crossover in the supercritical state. When the state of acetone spray passes through the transition region, the liquid-like and gas-like phases will have dramatic changes in the optical and macroscopic properties of spray (For example, when the injection temperature is equal to the critical temperature of 235 °C, the stable liquid-like areas crossing the pseudo-boiling line decreases by 9 times as much as that without crossing the pseudo-boiling line). The results of this paper have important reference values for the study of the supercritical spray atomization regime and the establishment of the simulation model.

An Approximate Parallel Vectors Operator for Multiple Vector Fields

AbstractThe Parallel Vectors (PV) Operator extracts the locations of points where two vector fields are parallel. In general, these features are line structures. The PV operator has been used successfully for a variety of problems, which include finding vortex‐core lines or extremum lines. We present a new generic feature extraction method for multiple 3D vector fields: The Approximate Parallel Vectors (APV) Operator extracts lines where all fields are approximately parallel. The definition of the APV operator is based on the application of PV for two vector fields that are derived from the given set of fields. The APV operator enables the direct visualization of features of vector field ensembles without processing fields individually and without causing visual clutter. We give a theoretical analysis of the APV operator and demonstrate its utility for a number of ensemble data.

Streamlines for Illustrative Real‐Time Rendering

AbstractLine drawing techniques are important methods to illustrate shapes. Existing feature line methods, e.g., suggestive contours, apparent ridges, or photic extremum lines, solely determine salient regions and illustrate them with separate lines. Hatching methods convey the shape by drawing a wealth of lines on the whole surface. Both approaches are often not sufficient for a faithful visualization of organic surface models, e.g., in biology or medicine. In this paper, we present a novel object‐space line drawing algorithm that conveys the shape of such surface models in real‐time. Our approach employs contour‐ and feature‐based illustrative streamlines to convey surface shape (ConFIS). For every triangle, precise streamlines are calculated on the surface with a given curvature vector field. Salient regions are detected by determining maxima and minima of a scalar field. Compared with existing feature lines and hatching methods, ConFIS uses the advantages of both categories in an effective and flexible manner. We demonstrate this with different anatomical and artificial surface models. In addition, we conducted a qualitative evaluation of our technique to compare our results with exemplary feature line and hatching methods.

Loci of extrema of thermodynamic response functions for the Lennard–Jones fluid

Lines of extrema along isotherms and isobars for the residual isochoric heat capacity, the residual isobaric heat capacity, the isobaric thermal expansivity, and the isothermal compressibility of the Lennard–Jones fluid have been studied from popular equations of state due to Johnson et al. [Mol. Phys. 78, 591 (1993)], Kolafa and Nezbeda [Fluid Phase Equilib. 100, 1 (1994)], and Mecke et al. [Int. J. Thermophys. 17, 391 (1996)]. On depicting such loci in the pressure–temperature plane, the characteristic behaviour of thermodynamic response functions in the ideal-gas limit (at high enough temperatures or low enough pressures), the close-packed-fluid limit (at low enough temperatures or high enough pressures) as well as in the liquid, critical, and supercritical regions is identified. The present analysis is informative itself, but it also stimulates further work in order to tackle more complicated cases of study including associated fluids.

Skeleton-based Adaptive In-between Generation for Hand-drawn Key Frames

For improving the efficiency of 2D animation production, this paper presents a method to create in-between frames based on hand-drawn key-frames. The outlines of characters or objects on two key-frames are used as inputs. First, a skeleton linkage of the target object is automatically constructed by rasterizing each of input key-frames and then applying a pixel-based skeleton extraction method. Secondary, a pair of skeleton linkages having corresponding structure between the current key-frame and the next key-frame is constructed by applying the stroke matching algorithm. After these processes, motion transitions between the skeleton linkages are generated based on our simulation model. When the in-between frames are created only in the 2D plane, the outlines at in-between frames can be generated by a 2D deformation. In case that the in-between transitions are containing a rotation around an axis which is no perpendicular to the drawing plane, however, a 3D structure is required. For achieving such in-between transitions, our method constructs a 3D structure by inflating 2D mesh based on the input outlines. Finally, the contours from the view-point for the created 3D structure are projected onto the 2D plane during in-between transitions. In our method, we adopt the Photic Extremum Lines (PEL) to extract the 2D contours from the obtained 3D shape. In this way, we achieve the in-between creation containing spatial rotation such as hand-flipping, which has not been achieved by general ways of in-between creation method.

Real-time computation of photic extremum lines (PELs)

Photic extremum lines (PELs) are view-dependent, object-space feature lines that characterize the significant changes of surface illumination. Though very effective for conveying 3D shapes, PELs are computationally expensive due to the heavy involvement of the third- and fourth-order derivatives. Also, they require the user to manually place a few auxiliary lights to depict the model details, which is usually tedious work. To overcome these challenges, we present a novel computational framework that improves both the speed and quality of PELs. First, we derive a simple, closed-form formula of gradient operator such that various orders of derivatives can be computed efficiently and in parallel using graphics processing units (GPUs). The GPU-based PEL extraction algorithm is one order of magnitude faster than the original one. Second, we propose to extract PELs from various non-photorealistic shadings that not only depict the overall shape but also bring out the details at different frequencies simultaneously. As a result, the user can easily control the relative emphasis to different scales and obtain the desired line drawing results. We demonstrate the improved PELs on a wide range of real-world objects.

Perceptual-saliency extremum lines for 3D shape illustration

Owing to their efficiency for conveying perceptual information of the underlying shape and their pleasing perceiving in visual aesthetics experience, line drawings are now becoming a widely used technique for illustrating 3D shapes. Using a center-surrounding bilateral filter operator on Gaussian-weighted average of local projection height between mesh vertices and their neighbors, a new perceptual-saliency measure which can depict surface salient features, is proposed in this paper. Due to the definition of perceptual-saliency measure, our perceptual-saliency extremum lines can be considered as the ridge-valley lines of perceptual-saliency measure along the principal curvature directions on triangular meshes. The experimental results demonstrate that these extremum lines effectively capture and depict 3D shape information visually, especially for archaeological artifacts.

An Effective Illustrative Visualization Framework Based on Photic Extremum Lines (PELs)

Conveying shape using feature lines is an important visualization tool in visual computing. The existing feature lines (e.g., ridges, valleys, silhouettes, suggestive contours, etc.) are solely determined by local geometry properties (e.g., normals and curvatures) as well as the view position. This paper is strongly inspired by the observation in human vision and perception that a sudden change in the luminance plays a critical role to faithfully represent and recover the 3D information. In particular, we adopt the edge detection techniques in image processing for 3D shape visualization and present Photic Extremum Lines (PELs) which emphasize significant variations of illumination over 3D surfaces. Comparing with the existing feature lines, PELs are more flexible and offer users more freedom to achieve desirable visualization effects. In addition, the user can easily control the shape visualization by changing the light position, the number of light sources, and choosing various light models. We compare PELs with the existing approaches and demonstrate that PEL is a flexible and effective tool to illustrate 3D surface and volume for visual computing.

Analyzing interference-fringe patterns by discriminating the features of wavelet maps of symmetric wavelets

This paper shows a connection between the lines of extrema of a three-dimensional wavelet map obtained by means of symmetric wavelets and the position of the fringes of an interference pattern. An algorithm is proposed that makes it possible to discriminate the lines of extrema of interference-fringe patterns