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  • Selected Abstracts


    Activation of receptors negatively coupled to adenylate cyclase is required for induction of long-term synaptic depression at Schaffer collateral-CA1 synapses

    DEVELOPMENTAL NEUROBIOLOGY, Issue 3 2006
    Linda A. Santschi
    Abstract Chemical LTD (CLTD) of synaptic transmission is triggered by simultaneously increasing presynaptic [cGMP] while inhibiting PKA. Here, we supply evidence that class II, but not III, metabotropic glutamate receptors (mGluRs), and A1 adenosine receptors, both negatively coupled to adenylate cyclase, play physiologic roles in providing PKA inhibition necessary to promote the induction of LTD at Schaffer collateral-CA1 synapses in hippocampal slices. Simultaneous activation of group II mGluRs with the selective agonist (2S,2,R,3,R)-2-(2,,3,-dicarboxy-cyclopropyl) glycine (DCGIV; 5 ,M), while raising [cGMP] with the type V phosphodiesterase inhibitor, zaprinast (20 ,M), resulted in a long-lasting depression of synaptic strength. When zaprinast (20 ,M) was combined with a cell-permeant PKA inhibitor H-89 (10 ,M), the need for mGluR IIs was bypassed. DCGIV, when combined with a "submaximal" low frequency stimulation (1 Hz/400 s), produced a saturating LTD. The mGluR II selective antagonist, (2S)-alpha-ethylglutamic acid (EGLU; 5 ,M), blocked induction of LTD by prolonged low frequency stimulation (1 Hz/900 s). In contrast, the mGluR III selective receptor blocker, (RS)-a-Cyclopropyl-[3- 3H]-4-phosphonophenylglycine (CPPG; 10 ,M), did not impair LTD. The selective adenosine A1 receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; 100 nM), also blocked induction of LTD, while the adenosine A1 receptor agonist N6 -cyclohexyl adenosine (CHA; 50 nM) significantly enhanced the magnitude of LTD induced by submaximal LFS and, when paired with zaprinast (20 ,M), was sufficient to elicit CLTD. Inhibition of PKA with H-89 rescued the expression of LTD in the presence of either EGLU or DPCPX, confirming the hypothesis that both group II mGluRs and A1 adenosine receptors enhance the induction of LTD by inhibiting adenylate cyclase and reducing PKA activity. 2005 Wiley Periodicals, Inc. J Neurobiol, 2006 [source]


    Stress reverses plasticity in the pathway projecting from the ventromedial prefrontal cortex to the basolateral amygdala

    EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2006
    Mouna Maroun
    Abstract We have previously shown that high-frequency stimulation to the basolateral amygdala (BLA) induces long-term potentiation (LTP) in the ventromedial prefrontal cortex (vmPFC) and that prior exposure to inescapable stress inhibits the induction of LTP in this pathway [Maroun & Richter-Levin (2003)J. Neurosci., 23, 4406,4409]. Here, we show that the reciprocal pathway projecting from the vmPFC to the BLA is resistant to the induction of LTP. Conversely, long-term depression (LTD) is robustly induced in the BLA in response to low-frequency stimulation to the vmPFC. Furthermore, prior exposure to inescapable stress reverses plasticity in this pathway, resulting in the promotion of LTP and the inhibition of LTD. Our findings suggest that, under normal and safe conditions, the vmPFC is unable to exert excitatory synaptic plasticity over the BLA; rather, LTD, which encodes memory of safety in the BLA, is favoured. Following stressful experiences, LTP in the BLA is promoted to encode memory of fear. [source]


    Hippocampal long-term depression as an index of spatial working memory

    EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2002
    Kazuhito Nakao
    Abstract Long-term potentiation (LTP), a form of synaptic plasticity in the hippocampus, is a cellular model for the neural basis of learning and memory, but few studies have investigated the contribution of long-term depression (LTD), a counterpart of LTP. To address the possible relationship between hippocampal LTD and spatial performance, the spatial cognitive ability of a rat was assessed in a spontaneous alternation test and, thereafter, LTD in response to low-frequency burst stimulation (LFBS) was monitored in the dentate gyrus of the same rat under anaesthesia. To enhance a divergence in the ability for spatial performance, some of the animals received fimbria,fornix (FF) transection 14 days before the experiments. LTD was reliably induced by application of LFBS to the medial perforant path of intact rats, while no apparent LTD was elicited in rats with FF lesions. The behavioural parameters of spatial memory showed a significant correlation with the magnitude of LTD. We found no evidence that the cognitive ability correlated with other electrophysiological parameters, e.g. basal synaptic responses, stimulus intensity to produce half-maximal responses, paired-pulse facilitation or paired-pulse depression. These results suggest that the magnitude of LTD in the dentate gyrus serves as a reliable index of spatial cognitive ability, providing insights into the functional significance of hippocampal LTD. [source]


    Differential induction of LTP and LTD is not determined solely by instantaneous calcium concentration: an essential involvement of a temporal factor

    EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2001
    Tomoyuki Mizuno
    Abstract Two opposite types of synaptic plasticity in the CA1 hippocampus, long-term potentiation (LTP) and long-term depression (LTD), require postsynaptic Ca2+ elevation. To explain these apparently contradictory phenomena, the current view assumes that a moderate postsynaptic increase in Ca2+ leads to LTD, whereas a large increase leads to LTP. No detailed study has so far been attempted to investigate whether the instantaneous Ca2+ elevation level differentially induces LTP or LTD. We therefore used low-frequency (1 Hz) stimulation of Schaffer collateral/commissural fibers in rat hippocampal slices, during a Mg2+ -free period, as the conditioning stimulus to investigate this. This allowed low-frequency afferent stimulation to cause a postsynaptic Ca2+ influx because the voltage-dependent block of N -methyl- d -aspartate (NMDA) receptor-channels by Mg2+ was removed. When delivered during the Mg2+ -free period, a single pulse, as well as 2,600 pulses, induced LTP that was occluded with tetanus-induced LTP. To decrease the Ca2+ influx, ,-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors were completely blocked by the addition of 10 m 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) to the conditioning medium, in which 1 Hz afferent stimuli (1,600 pulses) induced less LTP and never induced LTD. To further reduce the Ca2+ influx, NMDA receptors were partially blocked with d -(,)-2-amino-5-phosphonopentanoic acid (d -AP5). A small number of 1 Hz stimuli, however, never induced LTD. Only when the conditioning stimuli exceeded 200 pulses was LTD induced. The present findings provide definitive evidence that protracted conditioning is a prerequisite for the induction of LTD. Thus, not only the amplitude but also the duration of postsynaptic Ca2+ elevation could be essential factors for differentially inducing LTP or LTD. [source]


    Tyrosine phosphorylation of the GluR2 subunit is required for long-term depression of synaptic efficacy in young animals in vivo

    HIPPOCAMPUS, Issue 8 2007
    Christopher J. Fox
    Abstract The study of the intracellular mechanics that underlay changes in synaptic efficacy is a rapidly evolving field of research. It is currently believed that NMDA receptors play a significant role in the induction of synaptic plasticity, whereas AMPA receptors play a significant role in its expression. For AMPA receptors, it has been shown that tyrosine phosphorylation of the GluR2 carboxyl termini is required for the expression of long-term depression of synaptic efficacy (LTD) in vitro (Ahmadian et al. (2004) EMBO J 23:1040,1050). In the present study, we sought to determine whether similar mechanisms are involved in vivo, where different stimulation parameters are required for the induction of LTD. We initially used a paired-burst (PB) paradigm that reliably induces LTD in vivo. In these animals we were able to prevent the induction and expression of PB-LTD by administering a peptide (GluR-3Y) that acted as a competitive inhibitor of tyrosine phosphorylation. In a separate set of animals, we exposed animals to brief periods of stress (S) before using low-frequency stimuli to induce LTD (S-LTD). Again, GluR2,3Y blocked both the induction and expression of S-LTD. In contrast, an inert version of the peptide, with alanine replacing the three tyrosine residues, did not inhibit LTD induction. In addition, we demonstrated that GluR2,3Y did not affect the induction of long-term potentiation in vivo. These findings support the hypothesis that tyrosine phosphorylation and AMPA receptor endocytosis are necessary steps for the induction and maintenance of two forms of LTD in the CA1 region. 2007 Wiley-Liss, Inc. [source]


    Contribution of NR2A and NR2B NMDA subunits to bidirectional synaptic plasticity in the hippocampus in vivo

    HIPPOCAMPUS, Issue 11 2006
    Christopher J. Fox
    Abstract It has recently been proposed that activation of the NR2A subunit results in Long-term potentiation (LTP) induction, whereas activation of the NR2B subunit results in long-term depression (LTD) induction. The present study undertakes to replicate these findings in vivo to determine if a role for specific subunits in synaptic plasticity can be shown in the intact brain. Field recordings were made from the CA1 subfield of the hippocampus using Schaffer collateral stimulation in anesthetized male Sprague-Dawley rats. Antagonists of the N -methyl- D -aspartate receptors NR2A and NR2B subunits were administered by either intraperitoneal (i.p.) or intrahippocampal (i.h.) injections to assess their involvement in LTP (100 Hz stimuli) and LTD (200 Paired-burst stimuli). i.h. injection of Ro25,6981 (100 ,M) significantly attenuated hippocampal LTP expression and completely blocked LTD expression. When administered i.p., Ro25,6981 (6 mg/kg) again blocked LTD, but did not significantly diminish the expression of LTP. When NVP-AAM077 was administered i.h. (80 ,M) both LTP and LTD were completely abolished. The administration of this compound i.p. (1.2 mg/kg) also significantly attenuated LTP, but did not affect LTD. These data suggest that both NR2A and NR2B subunits can play roles in LTP and LTD in the hippocampus in vivo. 2006 Wiley-Liss, Inc. [source]


    Prenatal stress modifies hippocampal synaptic plasticity and spatial learning in young rat offspring

    HIPPOCAMPUS, Issue 5 2006
    Jianli Yang
    Abstract Clinical studies demonstrate that prenatal stress causes cognitive deficits and increases vulnerability to affective disorders in children and adolescents. The underlying mechanisms are not yet fully understood. Here, we reported that prenatal stress (10 unpredictable, 1 s, 0.8 mA foot shocks per day during gestational days 13,19) impaired long-term potentiation (LTP) but facilitated long-term depression (LTD) in hippocampal CA1 region in slices of the prenatal stressed offspring (5 weeks old). Cross-fostering neonate offspring by the prenatal stressed or control mothers did not change the effects of prenatal stress on the hippocampal LTP and LTD. Furthermore, prenatal stress enhanced the effects of acute stress on the hippocampal LTP and LTD and impaired spatial learning and memory in the Morris water maze in the young rat offspring. Therefore, prenatal stress alters synaptic plasticity and enhances the effects of acute stress on synaptic plasticity in the hippocampus, which may be the mechanism for the impaired spatial learning and memory in young rat offspring. 2006 Wiley-Liss, Inc. [source]


    Ethanol Acutely Modulates mGluR1-Dependent Long-Term Depression in Cerebellum

    ALCOHOLISM, Issue 7 2010
    Li-Da Su
    Background:, Acute and chronic ethanol exposure produces profound impairments in motor functioning. Individuals with lower sensitivity to the acute motor impairing effects of ethanol have an increased risk of developing alcohol dependence and abuse, and infants with subtle delays in motor coordination development may have an increased risk for subsequently developing alcoholism. Thus, understanding the mechanism by which ethanol disrupts motor functioning is very important. Methods:, Parasagittal slices of the cerebellar vermis (250 ,M thick) were prepared from P17 to 20 Sprague,Dawley rats. Whole-cell recordings of Purkinje cells were obtained with an Axopatch 200B amplifier. Parallel fiber-Purkinje cell synaptic currents were sampled at 1 kHz and digitized at 10 kHz, and synaptic long-term depression (LTD) was observed in either external or internal application of ethanol for comparison. Results:, We determined whether ethanol acutely affects parallel fiber LTD using whole-cell patch-clamp recordings from Purkinje cells. Application of ethanol both externally (50 mM) and internally (17 and 10 mM) significantly suppressed mGluR-mediate slow currents. Short-term external ethanol exposure (50 but not 17 mM) during tetanus blocked mGluR-dependent parallel fiber LTD. Furthermore, internal 17 and 10 mM ethanol completely inhibited this LTD. Conclusions:, The results of the current study demonstrate that ethanol acutely suppresses parallel fiber LTD and may influence the mGluR-mediated slow current intracellularly. This study, plus previous evidence by Carta and colleagues (2006) and Belmeguenai and colleagues (2008), suggests significant actions of ethanol on mGluR-mediated currents and its dependent plasticity in brain. [source]


    Haptic-constraint modeling based on interactive metaballs

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 5 2010
    Hui Chen
    Abstract Adding interactive haptic-constraint sensations is important in interactive computer gaming and 3D shape design. Usually constraints are set on vertices of the object to drive the deformation. How to simulate dynamic force constraints in interactive design is still a challenging task. In this paper, we propose a novel haptic-constraint modeling method based on interactive metaballs, during which the haptic-constraint tools are attracted to the target location and then control the touch-enabled deformation within the constrained areas. The interactive force feedbacks facilitate designers to accurately deform the target regions and fine carve the details as their intention on the objects. Our work studies how to apply touch sensation in such constrained deformations using interactive metaballs, thus users can truly feel and control the soft-touch objects during the deforming interactions. Experimental results show that the dynamic sense of touch during the haptic manipulation is intuitively simulated to users, via the interacting interface we have developed. Copyright 2010 John Wiley & Sons, Ltd. [source]


    A hybrid approach for simulating human motion in constrained environments

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2010
    Jia Pan
    Abstract We present a new algorithm to generate plausible motions for high-DOF human-like articulated figures in constrained environments with multiple obstacles. Our approach is general and makes no assumptions about the articulated model or the environment. The algorithm combines hierarchical model decomposition with sample-based planning to efficiently compute a collision-free path in tight spaces. Furthermore, we use path perturbation and replanning techniques to satisfy the kinematic and dynamic constraints on the motion. In order to generate realistic human-like motion, we present a new motion blending algorithm that refines the path computed by the planner with motion capture data to compute a smooth and plausible trajectory. We demonstrate the results of generating motion corresponding to placing or lifting object, walking, and bending for a 38-DOF articulated model. Copyright 2010 John Wiley & Sons, Ltd. [source]


    Choreographing emotional facial expressions

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2010
    Robin J.S. Sloan
    Abstract While much is known about the appearance and human perception of emotional facial expressions, researchers and professionals experience difficulties when attempting to create believable animated characters. Methods for automating or capturing dynamic facial expressions have come on in leaps and bounds in recent years, resulting in increasingly realistic characters. However, accurate replication of naturalistic movement does not necessarily ensure authentic character performance. In this paper, the authors present a project which makes use of creative animation practices and artistic reflection as methods of research. The output of animation practice is tested experimentally by measuring observer perception and comparing the results with artistic observations and predictions. Ultimately, the authors aim to demonstrate that animation practice can generate new knowledge about dynamic character performance, and that arts-based methods can and should be considered valuable tools in a field often dominated by technical methods of research. Copyright 2010 John Wiley & Sons, Ltd. [source]


    Situation agents: agent-based externalized steering logic

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2010
    Matthew Schuerman
    Abstract We present a simple and intuitive method for encapsulating part of agents' steering and coordinating abilities into a new class of agents, called situation agents. Situation agents have all the abilities of typical agents. In addition, they can influence the steering decisions of any agent, including other situation agents, within their sphere of influence. Encapsulating steering logic into moving agents is a powerful abstraction which provides more flexibility and efficiency than traditional informed environment approaches, and works with many of the current steering methodologies. We demonstrate our proposed approach in a number of challenging scenarios. Copyright 2010 John Wiley & Sons, Ltd. [source]


    Inhomogeneous volumetric Laplacian deformation for rhinoplasty planning and simulation system

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2010
    Sheng-hui Liao
    Abstract This paper presents an intuitive rhinoplasty planning and simulation system, to provide high quality prediction of postoperative appearance, and design patient specific nose prosthesis automatically. The key component is a novel volumetric Laplacian deformation tool inspired by the state-of-the-art differential surface deformation techniques. Working on the volumetric domain and incorporating inhomogeneous material from CT data make the new approach suitable for soft tissue simulation. In particular, the system employs a special sketch contour driving deformation interface, which can provide realistic 3D rhinoplasty simulation with intuitive and straightforward 2D manipulation. When satisfied with the appearance, the change of soft tissue before and after simulation is utilized to generate the individual prosthesis model automatically. Clinical validation using post-operative CT data demonstrated that the system can provide prediction results of high quality. And the surgeons who used the system confirmed that this planning system is attractive and has potential for daily clinical practice. Copyright 2010 John Wiley & Sons, Ltd. [source]


    Volume fraction based miscible and immiscible fluid animation

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2010
    Kai Bao
    Abstract We propose a volume fraction based approach to effectively simulate the miscible and immiscible flows simultaneously. In this method, a volume fraction is introduced for each fluid component and the mutual interactions between different fluids are simulated by tracking the evolution of the volume fractions. Different techniques are employed to handle the miscible and immiscible interactions and special treatments are introduced to handle flows involving multiple fluids and different kinds of interactions at the same time. With this method, second-order accuracy is preserved in both space and time. The experiment results show that the proposed method can well handle both immiscible and miscible interactions between fluids and much richer mixing detail can be generated. Also, the method shows good controllability. Different mixing effects can be obtained by adjusting the dynamic viscosities and diffusion coefficients. Copyright 2010 John Wiley & Sons, Ltd. [source]


    Stable stylized wireframe rendering

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2010
    Chen Tang
    Abstract Stylized wireframe rendering of 3D model is widely used in animation software in order to depict the configuration of deformable model in comprehensible ways. However, since some inherent flaws in traditional depth test based rendering technology, shape of lines can not been preserved as continuous movement or deformation of models. There often exists severe aliasing like flickering artifact when objects rendered in line form animate, especially rendered with thick or dashed line. To cover this artifact, unlike traditional approach, we propose a novel fast line drawing method with high visual fidelity for wireframe depiction which only depends on intrinsic topology of primitives without any preprocessing step or extra adjacent information pre-stored. In contrast to previous widely-used solutions, our method is advantageous in highly accurate visibility, clear and stable line appearance without flickering even for thick and dashed lines with uniform width and steady configuration as model moves or animates, so that it is strongly suitable for animation system. In addition, our approach can be easily implemented and controlled without any additional preestimate parameters supplied by users. Copyright 2010 John Wiley & Sons, Ltd. [source]


    Virtual humans elicit socially anxious interactants' verbal self-disclosure

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2010
    Sin-Hwa Kang
    Abstract We explored the relationship between interactants' social anxiety and the interactional fidelity of virtual humans. We specifically addressed whether the contingent non-verbal feedback of virtual humans affects the association between interactants' social anxiety and their verbal self-disclosure. This subject was investigated across three experimental conditions where participants interacted with real human videos and virtual humans in computer-mediated interview interactions. The results demonstrated that socially anxious people revealed more information and greater intimate information about themselves when interacting with a virtual human when compared with real human video interaction, whereas less socially anxious people did not show this difference. We discuss the implication of this association between the interactional fidelity of virtual humans and social anxiety in a human interactant on the design of an embodied virtual agent for social skills' training and psychotherapy. Copyright 2010 John Wiley & Sons, Ltd. [source]


    Interactive animation of virtual humans based on motion capture data

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 5-6 2009
    Franck Multon
    Abstract This paper presents a novel, parameteric framework for synthesizing new character motions from existing motion capture data. Our framework can conduct morphological adaptation as well as kinematic and physically-based corrections. All these solvers are organized in layers in order to be easily combined together. Given locomotion as an example, the system automatically adapts the motion data to the size of the synthetic figure and to its environment; the character will correctly step over complex ground shapes and counteract with external forces applied to the body. Our framework is based on a frame-based solver. This ensures animating hundreds of humanoids with different morphologies in real-time. It is particularly suitable for interactive applications such as video games and virtual reality where a user interacts in an unpredictable way. Copyright 2009 John Wiley & Sons, Ltd. [source]


    Combined compression and simplification of dynamic 3D meshes

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 4 2009
    Libor V
    Abstract We present a new approach to dynamic mesh compression, which combines compression with simplification to achieve improved compression results, a natural support for incremental transmission and level of detail. The algorithm allows fast progressive transmission of dynamic 3D content. Our scheme exploits both temporal and spatial coherency of the input data, and is especially efficient for the case of highly detailed dynamic meshes. The algorithm can be seen as an ultimate extension of the clustering and local coordinate frame (LCF)-based approaches, where each vertex is expressed within its own specific coordinate system. The presented results show that we have achieved better compression efficiency compared to the state of the art methods. Copyright 2008 John Wiley & Sons, Ltd. [source]


    Spatial camera orientation control by rotation-minimizing directed frames

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 4 2009
    Rida T. Farouki
    Abstract The use of rotation-minimizing directed frames (RMDFs) for defining smoothly varying camera orientations along given spatial paths, in real or virtual environments, is proposed. A directed frame on a space curve is a varying orthonormal basis for ,3 such that coincides with the unit polar vector from the origin to each curve point, and such a frame is rotation-minimizing if its angular velocity vector maintains a vanishing component along o. To facilitate computation of rotation-minimizing directed frames, it is shown that the basic theory is equivalent to the established theory for rotation-minimizing adapted frames,for which one frame vector coincides with the tangent at each curve point,if one replaces the given space curve by its anti-hodograph (i.e., indefinite integral). A family of polynomial curves on which RMDFs can be computed exactly by a rational function integration, the Pythagorean (P) curves, is also introduced, together with algorithms for their construction. Copyright 2009 John Wiley & Sons, Ltd. [source]


    Stylized lighting for cartoon shader

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 2-3 2009
    Hideki Todo
    Abstract In the context of non-photorealistic imaging, such as digital cel animation, lighting is symbolic and stylized to depict the scene's mood and the geometric or physical features of the objects in the scene. Stylized light and shade should therefore be intentionally animated rather than rigorously simulated. However, it is difficult to achieve smooth animation of light and shade that are stylized with a user's intention, because such stylization cannot be achieved using just conventional 3D lighting. To address this problem, we propose a 3D stylized lighting method, focusing on several stylized effects including straight lighting, edge lighting, and detail lighting which are important features in hand-drawn cartoon animation. Our method is an extension of the conventional cartoon shader and introduces a light coordinate system for light shape control with smooth animations of light and shade. We also extend a toon mapping process for detailed feature lighting. Having these algorithms in a real-time cartoon shader, our prototype system allows the interactive creation of stylized lighting animations. We show several animation results obtained by our method to illustrate usefulness and effectiveness of our method. Copyright 2009 John Wiley & Sons, Ltd. [source]


    Furstyling on angle-split shell textures

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 2-3 2009
    Bin Sheng
    Abstract This paper presents a new method for modeling and rendering fur with a wide variety of furstyles. We simulate virtual fur using shell textures,a multiple layers of textured slices for its generality and efficiency. As shell textures usually suffer from the inherent visual gap errors due to the uniform discretization nature, we present the angle-split shell textures (ASST) approach, which classifies the shell textures into different types with different numbers of texture layers, by splitting the angle space of the viewing angles between fur orientation and view direction. Our system can render the fur with biological patterns, and utilizes vector field and scalar field on ASST to control the geometric variations of the furry shape. Users can intuitively shape the fur by applying the combing, blowing, and interpolating effects in real time. Our approach is intuitive to implement without using complex data structures, with real-time performance for dynamic fur appearances. Copyright 2009 John Wiley & Sons, Ltd. [source]


    Perceptual 3D pose distance estimation by boosting relational geometric features

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 2-3 2009
    Cheng Chen
    Abstract Traditional pose similarity functions based on joint coordinates or rotations often do not conform to human perception. We propose a new perceptual pose distance: Relational Geometric Distance that accumulates the differences over a set of features that reflects the geometric relations between different body parts. An extensive relational geometric feature pool that contains a large number of potential features is defined, and the features effective for pose similarity estimation are selected using a set of labeled data by Adaboost. The extensive feature pool guarantees that a wide diversity of features is considered, and the boosting ensures that the selected features are optimized when used jointly. Finally, the selected features form a pose distance function that can be used for novel poses. Experiments show that our method outperforms others in emulating human perception in pose similarity. Our method can also adapt to specific motion types and capture the features that are important for pose similarity of a certain motion type. Copyright 2009 John Wiley & Sons, Ltd. [source]


    Fast simulation of skin sliding

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 2-3 2009
    Xiaosong Yang
    Abstract Skin sliding is the phenomenon of the skin moving over underlying layers of fat, muscle and bone. Due to the complex interconnections between these separate layers and their differing elasticity properties, it is difficult to model and expensive to compute. We present a novel method to simulate this phenomenon at real-time by remeshing the surface based on a parameter space resampling. In order to evaluate the surface parametrization, we borrow a technique from structural engineering known as the force density method (FDM)which solves for an energy minimizing form with a sparse linear system. Our method creates a realistic approximation of skin sliding in real-time, reducing texture distortions in the region of the deformation. In addition it is flexible, simple to use, and can be incorporated into any animation pipeline. Copyright 2009 John Wiley & Sons, Ltd. [source]


    Interactive shadowing for 2D Anime

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 2-3 2009
    Eiji Sugisaki
    Abstract In this paper, we propose an instant shadow generation technique for 2D animation, especially Japanese Anime. In traditional 2D Anime production, the entire animation including shadows is drawn by hand so that it takes long time to complete. Shadows play an important role in the creation of symbolic visual effects. However shadows are not always drawn due to time constraints and lack of animators especially when the production schedule is tight. To solve this problem, we develop an easy shadowing approach that enables animators to easily create a layer of shadow and its animation based on the character's shapes. Our approach is both instant and intuitive. The only inputs required are character or object shapes in input animation sequence with alpha value generally used in the Anime production pipeline. First, shadows are automatically rendered on a virtual plane by using a Shadow Map1 based on these inputs. Then the rendered shadows can be edited by simple operations and simplified by the Gaussian Filter. Several special effects such as blurring can be applied to the rendered shadow at the same time. Compared to existing approaches, ours is more efficient and effective to handle automatic shadowing in real-time. Copyright 2009 John Wiley & Sons, Ltd. [source]


    Coherence aware GPU-based ray casting for virtual colonoscopy

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 1 2009
    Taek Hee Lee
    Abstract In this paper, we propose a GPU-based volume ray casting for virtual colonoscopy to generate high-quality rendering images with a large screen size. Using the temporal coherence for ray casting, the empty space leaping can be efficiently done by reprojecting first-hit points of the previous frame; however, these approaches could produce artifacts such as holes or illegal starting positions due to the insufficient resolution of first-hit points. To eliminate these artifacts, we use a triangle mesh of first-hit points and check the intersection of each triangle with the corresponding real surface. Illegal starting positions can be avoided by replacing a false triangle cutting the real surface with five newly generated triangles. The proposed algorithm is best fit to the recent GPU architecture with Shader Model 4.0 which supports not only fast rasterization of a triangle mesh but also many flexible vertex operations. Experimental results on ATI 2900 with DirectX10 show perspective volume renderings of over 24fps on 1024,,1024 screen size without any loss of image quality. Copyright 2008 John Wiley & Sons, Ltd. [source]


    GPU-based interactive visualization framework for ultrasound datasets

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 1 2009
    Sukhyun Lim
    Abstract Ultrasound imaging is widely used in medical areas. By transmitting ultrasound signals into the human body, their echoed signals can be rendered to represent the shape of internal organs. Although its image quality is inferior to that of CT or MR, ultrasound is widely used for its speed and reasonable cost. Volume rendering techniques provide methods for rendering the 3D volume dataset intuitively. We present a visualization framework for ultrasound datasets that uses programmable graphics hardware. For this, we convert ultrasound coordinates into Cartesian form. In ultrasound datasets, however, since physical storage and representation space is different, we apply different sampling intervals adaptively for each ray. In addition, we exploit multiple filtered datasets in order to reduce noise. By our method, we can determine the adequate filter size without considering the filter size. As a result, our approach enables interactive volume rendering for ultrasound datasets, using a consumer-level PC. Copyright 2009 John Wiley & Sons, Ltd. [source]


    A comparative study of awareness methods for peer-to-peer distributed virtual environments

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 5 2008
    S. Rueda
    Abstract The increasing popularity of multi-player online games is leading to the widespread use of large-scale Distributed Virtual Environments (DVEs) nowadays. In these systems, peer-to-peer (P2P) architectures have been proposed as an efficient and scalable solution for supporting massively multi-player applications. However, the main challenge for P2P architectures consists of providing each avatar with updated information about which other avatars are its neighbors. This problem is known as the awareness problem. In this paper, we propose a comparative study of the performance provided by those awareness methods that are supposed to fully solve the awareness problem. This study is performed using well-known performance metrics in distributed systems. Moreover, while the evaluations shown in the literature are performed by executing P2P simulations on a single (sequential) computer, this paper evaluates the performance of the considered methods on actually distributed systems. The evaluation results show that only a single method actually provides full awareness to avatars. This method also provides the best performance results. Copyright 2008 John Wiley & Sons, Ltd. [source]


    Generalized minimum-norm perspective shadow maps

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 5 2008
    Fan Zhang
    Abstract Shadow mapping has been extensively used for real-time shadow rendering in 3D computer games, though it suffers from the inherent aliasing problems due to its image-based nature. This paper presents an enhanced variant of light space perspective shadow maps to optimize perspective aliasing distribution in possible general cases where the light and view directions are not orthogonal. To be mathematically sound, the generalized representation of perspective aliasing errors has been derived in detail. Our experiments have shown the enhanced shadow quality using our algorithm in dynamic scenes. Copyright 2008 John Wiley & Sons, Ltd. [source]


    Directable animation of elastic bodies with point-constraints

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2008
    Ryo Kondo
    Abstract We propose a simple framework for making elastic body animation with point constraints. In general, a physics-based approach for constraint animation offers a variety of animations with physically correct realism, which are achieved by solving the equations of motion. However, in the digital animation industry, solving the equations of motion is an indirect path to creating more art-directed animations that maintain a plausible realism. Our algorithms provide animators a practical way to make elastic body animation with plausible realism, while effectively using point-constraints to offer directatorial control. The animation examples illustrate that our framework creates a wide variety of point-constraint animations of elastic objects with greater directability than existing methods. Copyright 2008 John Wiley & Sons, Ltd. [source]


    Extended spatial keyframing for complex character animation

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2008
    Byungkuk Choi
    Abstract As 3D computer animation becomes more accessible to novice users, it makes it possible for these users to create high-quality animations. This paper introduces a more powerful system to create highly articulated character animations with an intuitive setup then the previous research, Spatial Keyframing (SK). As the main purpose of SK was the rapid generation of primitive animation over quality animation, we propose Extended Spatial Keyframing (ESK) that exploits a global control structure coupled with multiple sets of spatial keyframes, and hierarchical relationship between controllers. The generated structure can be flexibly embedded into the given rigged character, and the system enables the given character to be animated delicately by user performance. During the performance, the movement of the highest ranking controllers across the control hierarchy is recorded in layered style to increase the level of detail for final motions. Copyright 2008 John Wiley & Sons, Ltd. [source]