bluuebunny/crossref_metadata_2025 huggingface dataset:
Zirconia‐implant‐supported all‐ceramic crowns withstand long‐term load: a pilot investigation
Authors: Kohal Ralf‐J. , Klaus Gerold , Strub Jörg R.
Published: July 2006

Objectives: The purpose of this pilot investigation was to test whether zirconia implants restored with different all‐ceramic crowns would fulfill the biomechanical requirements for clinical use. Therefore, all‐ceramic Empress®‐1 and Procera® crowns were cemented on zirconia implants and exposed to the artificial mouth. Afterwards, the fracture strength of the all‐ceramic implant–crown systems was evaluated. Conventional titanium implants restored with porcelain‐fused‐to‐metal (PFM) crowns served as controls.

Material and methods: Sixteen titanium implants with 16 PFM crowns and 32 zirconia implants with 16 Empress®‐1 crowns and 16 Procera® crowns each—i.e., three implant–crown groups—were used in this investigation. The titanium implants were fabricated using the ReImplant® system and the zirconia implants using the Celay® system. The upper left central incisor served as a model for the fabrication of the implants and the crowns. Eight samples of each group were submitted to a long‐term load test in the artificial mouth (1.2 million chewing cycles). Subsequently, a fracture strength test was performed with seven of the eight crowns. The remaining eight samples of each group were not submitted to the long‐term load in the artificial mouth but were fracture‐tested immediately. One loaded and one unloaded sample of each group were evaluated regarding the marginal fit of the crowns.

Results: All test samples survived the exposure to the artificial mouth. Three Empress®‐1 crowns showed cracks in the area of the loading steatite ball. The values for the fracture load in the titanium implant–PFM crown group without artificial loading ranged between 420 and 610 N (mean: 531.4 N), between 460 and 570 N (mean: 512.9 N) in the Empress®‐1 crown group, and in the Procera® crown group the values were between 475 and 700 N (mean: 575.7 N) when not loaded artificially. The results when the specimens were loaded artificially with 1.2 million cycles were as follows: the titanium implant–PFM crowns fractured between 440 and 950 N (mean: 668.6 N), the Empress®‐1 crowns between 290 and 550 N (mean: 410.7 N), and the Procera® crowns between 450 and 725 N (mean: 555.5 N). No statistically significant differences could be found among the groups without artificial load. The fracture values for the PFM and the Procera® crowns after artificial loading were statistically significantly higher than that for the loaded Empress®‐1 crowns. There was no significant difference between the PFM crown group and the Procera® group.

Conclusions: Within the limits of this pilot investigation, it seems that zirconia implants restored with the Procera® crowns possibly fulfill the biomechanical requirements for anterior teeth. However, further investigations with larger sample sizes have to confirm these preliminary results. As three Empress®‐1 crowns showed crack development in the loading area of the steatite balls in the artificial mouth, their clinical use on zirconia implants has to be questioned.
Ecology of larval blue sucker (Cycleptus elongatus) in the Mississippi River
Authors: Adams S. R. , Flinn M. B. , Burr B. M. , Whiles M. R. , Garvey J. E.
Published: July 2006

Abstract –  Ecology of larval blue sucker, Cycleptus elongatus, a North American catostomid that has declined throughout its range, is poorly known because larvae have rarely been sampled. A total of 316 young blue suckers (16.0–39.0 mm total length) was captured over 3 years at 14 off‐channel sites in Pool 25, Mississippi River. Blue suckers demonstrated distinct temporal and spatial abundance patterns. Blue suckers were only captured in late May/early June, and were more abundant during a year of little flooding. Abundance was correlated with the distance a site was from the main channel, being highest in island borders and island sloughs in proximity to the channel. Fish guts contained a relatively high biomass of chironomids and zooplankton, suggesting islands were providing suitable feeding opportunities. Because of their proximity to flows, slack waters provided by islands were accessible to blue sucker larvae dispersing from channel spawning areas and facilitated their development into rheophilic juveniles.
Seasonality of psychopathology and circannual melatonin rhythm
Authors: Morera A.L. , Abreu P.
Published: July 2006

Abstract:  The association of seasonal changes in health and disease has been known for centuries. The prevalence of psychopathological symptoms with seasonal fluctuations and the use of melatonin as a biological marker of circadian and circannual rhythms is well documented. The aim of this work was to study the variability of melatonin secretion between summer and winter in our geographical area (28°N, 16°W) and relate the changes to the level of psychopathology. Ten drug‐free, nonsmoker, healthy subjects were studied in summer (August) and winter (December). Blood samples for melatonin assays were collected every hour at night for 5 hr, from 22:00 to 02:00 hr, and next day at noon. Melatonin was assayed by an ELISA technique. Psychopathology was evaluated by means of the 28‐item version of the General Health Questionnaire (GHQ‐28). All subjects had a circadian rhythm of melatonin secretion in summer and winter. There was a seasonal rhythm with melatonin levels being significantly higher at night in winter than in summer. Melatonin levels at 22:00, 23:00, 24:00 and 01:00 hr and mean melatonin area under the curve (AUC) were significantly higher in winter than in summer. Melatonin AUC increased 80% in winter compared with summer. The GHQ‐28 somatic and anxiety subscales and the total GHQ‐28 score were significantly higher in winter than summer. Psychopathology scores were significantly and negatively correlated with melatonin production in summer and winter. Our data strongly suggest that melatonin production and psychopathology levels present seasonal fluctuations and these variations should be taken into account when conducting research in this field.
Decidability results for sets with atoms
Authors: Dovier Agostino , Formisano Andrea , Omodeo Eugenio G.
Published: July 2006

Formal set theory is traditionally concerned with
pure
sets; consequently, the satisfiability problem for fragments of set theory was most often addressed (and in many cases positively solved) in the pure framework. In practical applications, however, it is common to assume the existence of a number of primitive objects (sometimes called
atoms
) that can be members of sets but behave differently from them. If these entities are assumed to be devoid of members, the standard extensionality axiom must be revised; then decidability results can sometimes be achieved via reduction to the pure case and sometimes can be based on direct goal-driven algorithms. An alternative approach to modeling atoms that allows one to retain the original formulation of extensionality was proposed by Quine: atoms are self-singletons. In this article we adopt this approach in coping with the satisfiability problem: We show the decidability of this problem relativized to ∃*∀-sentences, and develop a goal-driven unification algorithm.
Ordinary interactive small-step algorithms, I
Authors: Blass Andreas , Gurevich Yuri
Published: July 2006

This is the first in a series of articles extending the abstract state machine thesis---that arbitrary algorithms are behaviorally equivalent to abstract state machines---to algorithms that can interact with their environments during a step rather than only between steps. In the present work, we describe, by means of suitable postulates, those interactive algorithms that (1) proceed in discrete, global steps; (2) perform only a bounded amount of work in each step; (3) use only such information from the environment as can be regarded as answers to queries; and (4) never complete a step until all queries from that step have been answered.We indicate how a great many sorts of interaction meet these requirements. We also discuss in detail the structure of queries and replies and the appropriate definition of equivalence of algorithms.Finally, motivated by our considerations concerning queries, we discuss a generalization of first-order logic in which the arguments of function and relation symbols are not merely tuples of elements but orbits of such tuples under groups of permutations of the argument places.
Conjunctive queries over trees
Authors: Gottlob Georg , Koch Christoph , Schulz Klaus U.
Published: July 2006

We study the complexity and expressive power of conjunctive queries over unranked labeled trees represented using a variety of structure relations such as “child”, “descendant”, and “following” as well as unary relations for node labels. We establish a framework for characterizing structures representing trees for which conjunctive queries can be evaluated efficiently. Then we completely chart the tractability frontier of the problem and establish a dichotomy theorem for our axis relations, that is, we find all subset-maximal sets of axes for which query evaluation is in polynomial time and show that for all other cases, query evaluation is NP-complete. All polynomial-time results are obtained immediately using the proof techniques from our framework. Finally, we study the expressiveness of conjunctive queries over trees and show that for each conjunctive query, there is an equivalent acyclic positive query (i.e., a set of acyclic conjunctive queries), but that in general this query is not of polynomial size.
The interpretation and utility of three cohesion metrics for object-oriented design
Authors: Counsell Steve , Swift Stephen , Crampton Jason
Published: July 2006

The concept of cohesion in a class has been the subject of various recent empirical studies and has been measured using many different metrics. In the structured programming paradigm, the software engineering community has adopted an informal yet meaningful and understandable definition of cohesion based on the work of Yourdon and Constantine. The object-oriented (OO) paradigm has formalised various cohesion measures, but the argument over the most meaningful of those metrics continues to be debated. Yet achieving highly cohesive software is fundamental to its comprehension and thus its maintainability. In this article we subject two object-oriented cohesion metrics, CAMC and NHD, to a rigorous mathematical analysis in order to better understand and interpret them. This analysis enables us to offer substantial arguments for preferring the NHD metric to CAMC as a measure of cohesion. Furthermore, we provide a complete understanding of the behaviour of these metrics, enabling us to attach a meaning to the values calculated by the CAMC and NHD metrics. In addition, we introduce a variant of the NHD metric and demonstrate that it has several advantages over CAMC and NHD. While it may be true that a generally accepted formal and informal definition of cohesion continues to elude the OO software engineering community, there seems considerable value in being able to compare, contrast, and interpret metrics which attempt to measure the same features of software.
Locking under Pfair scheduling
Authors: Holman Philip , Anderson James H.
Published: July 2006

We present several locking synchronization protocols for Pfair-scheduled multiprocessor systems. We focus on two classes of protocols. The first class is only applicable in systems in which all critical sections are short relative to the length of the scheduling quantum. In this case, efficient synchronization can be achieved by ensuring that all locks have been released before tasks are preempted. This is accomplished by exploiting the quantum-based nature of Pfair scheduling, which provides
a priori
knowledge of all possible preemption points. The second and more general protocol class is applicable to any system. For this class, we consider the use of a client-server model. We also discuss the viability of inheritance-based protocols in Pfair-scheduled systems.
A formal method for hardware IP design and integration under I/O and timing constraints
Authors: Coussy Philippe , Casseau Emmanuel , Bomel Pierre , Baganne Adel , Martin Eric
Published: July 2006

IP integration, which is one of the most important SoC design steps, requires taking into account communication and timing constraints. In that context, design and reuse can be improved using IP cores described at a high abstraction level. In this paper, we present an IP design approach that relies on three main phases: (1) constraint modeling, (2) IP constraint analysis steps for feasibility checking, and (3) synthesis. We propose a set of techniques dedicated to the digital signal processing domain that lead to an optimized IP core integration. Based on a generic architecture of components, the method we propose provides automatic generation of IP cores designed under integration constraints. We show the effectiveness of our approach with a DCT core design case study.
Reducing code size through address register assignment
Authors: Chen G. , Kandemir M. , Irwin M. J. , Ramanujam J.
Published: July 2006

In DSP processors, minimizing the amount of address calculations is critical for reducing code size and improving performance, since studies of programs have shown that instructions that manipulate address registers constitute a significant portion of the overall instruction count (up to 55%). This work presents a compiler-based optimization strategy to “reduce the code size in embedded systems.” Our strategy maximizes the use of indirect addressing modes with postincrement/decrement capabilities available in DSP processors. These modes can be exploited by ensuring that successive references to variables access consecutive memory locations. To achieve this spatial locality, our approach uses both access pattern modification (program code restructuring) and memory storage reordering (data layout restructuring). Experimental results on a set of benchmark codes show the effectiveness of our solution and indicate that our approach outperforms the previous approaches to the problem. In addition to resulting in significant reductions in instruction memory (storage) requirements, the proposed technique improves execution time.
Recovery code generation for general speculative optimizations
Authors: Lin Jin , Hsu Wei-Chung , Yew Pen-Chung , Ju Roy Dz-Ching , Ngai Tin-Fook
Published: July 2006

A general framework that integrates both control and data speculation using alias profiling and/or compiler heuristic rules has shown to improve CPU2000 performance on Itanium systems. However, speculative optimizations require check instructions and recovery code to ensure correct execution when speculation fails at runtime. How to generate check instructions and their associated recovery code efficiently and effectively is an issue yet to be well studied. It is also, very important that the recovery code generated in the earlier phases integrate gracefully in the later optimization phases. At the very least, it should not hinder later optimizations, thus, ensuring overall performance improvement. This paper proposes a framework that uses an
if-block
structure to facilitate check instructions and recovery code generation for general speculative optimizations. It allows speculative instructions and their recovery code generated in the early compiler optimization phases to be integrated effectively with the subsequent optimization phases. It also allows
multilevel speculation
for multilevel pointers and multilevel expression trees to be handled with no additional complexity. The proposed recovery code generation framework has been implemented and evaluated in the Open Research Compiler (ORC).
Global software piracy
Authors: Bagchi Kallol , Kirs Peeter , Cerveny Robert
Published: July 2006

Searching for explanations to increasing global software piracy rates.
Piracy, computer crime, and IS misuse at the university
Authors: Cronan Timothy Paul , Foltz C. Bryan , Jones Thomas W.
Published: July 2006

Who commits software misuse? Knowing the answer to this question will help organizations protect their information systems.
Introduction
Authors: Conti Gregory
Published: July 2006

Why computer science should pay serious attention to the hacking community and its passion for pushing the limits of technology and its role as a counterbalance to its misuse.
Academic freedom and the hacker ethic
Authors: Cross Tom
Published: July 2006

Hackers advocate the free pursuit and sharing of knowledge without restriction, even as they acknowledge that applying it is something else.
Research lessons from hardware hacking
Authors: Grand Joe
Published: July 2006

Want to know how something works? Tear it apart. Along the way, you might learn to improve it or make it do something it was never intended to do.
Representing and querying XML with incomplete information
Authors: Abiteboul Serge , Segoufin Luc , Vianu Victor
Published: July 2006

We study the representation and querying of XML with incomplete information. We consider a simple model for XML data and their DTDs, a very simple query language, and a representation system for incomplete information in the spirit of the representations systems developed by Imielinski and Lipski [1984] for relational databases. In the scenario we consider, the incomplete information about an XML document is continuously enriched by successive queries to the document. We show that our representation system can represent partial information about the source document acquired by successive queries, and that it can be used to intelligently answer new queries. We also consider the impact on complexity of enriching our representation system or query language with additional features. The results suggest that our approach achieves a practically appealing balance between expressiveness and tractability.
Sequencing XML data and query twigs for fast pattern matching
Authors: Rao Praveen , Moon Bongki
Published: July 2006

We propose a new way of indexing XML documents and processing twig patterns in an XML database. Every XML document in the database can be transformed into a sequence of labels by prüfer's method that constructs a one-to-one correspondence between trees and sequences. During query processing, a twig pattern is also transformed into its Prüfer sequence. By performing subsequence matching on the set of sequences in the database and performing a series of refinement phases that we have developed, we can find all the occurrences of a twig pattern in the database. Our approach allows
holistic processing
of a twig pattern without breaking the twig into root-to-leaf paths and processing these paths individually. Furthermore, we show in the article that all correct answers are found without any false dismissals or false alarms. Experimental results demonstrate the performance benefits of our proposed techniques.
Adaptive information extraction
Authors: Turmo Jordi , Ageno Alicia , Català Neus
Published: July 2006

The growing availability of online textual sources and the potential number of applications of knowledge acquisition from textual data has lead to an increase in Information Extraction (IE) research. Some examples of these applications are the generation of data bases from documents, as well as the acquisition of knowledge useful for emerging technologies like question answering, information integration, and others related to text mining. However, one of the main drawbacks of the application of IE refers to its intrinsic domain dependence. For the sake of reducing the high cost of manually adapting IE applications to new domains, experiments with different Machine Learning (ML) techniques have been carried out by the research community. This survey describes and compares the main approaches to IE and the different ML techniques used to achieve Adaptive IE technology.
Constructing memory-minimizing schedules for multifrontal methods
Authors: Guermouche Abdou , L'excellent Jean-Yves
Published: July 2006

We are interested in the memory usage of multifrontal methods. Starting from the algorithms introduced by Liu, we propose new schedules to allocate and process tasks that improve memory usage. This generalizes two existing factorization and memory-allocation schedules by allowing a more flexible task allocation together with a specific tree traversal. We present optimal algorithms for this new class of schedules, and demonstrate experimentally their benefit for some real-world matrices from sparse matrix collections where either the active memory or the total memory is minimized.
Algorithm 850
Authors: Gil Amparo , Segura Javier , Temme Nico M.
Published: July 2006

Fortran 90 programs for the computation of real parabolic cylinder functions are presented. The code computes the functions
U
(
a
,
x
),
V
(
a
,
x
) and their derivatives for real
a
and
x
(
x
≥ 0). The code also computes scaled functions. The range of computation for scaled PCFs is practically unrestricted. The aimed relative accuracy for scaled functions is better than 5 10
−14
. Exceptions to this accuracy are the evaluation of the functions near their zeros and the error caused by the evaluation of trigonometric functions of large arguments when |a| >
x
. The routines always give values for which the Wronskian relation for scaled functions is verified with a relative accuracy better than 5 10
−14
. The accuracy of the unscaled functions is also better than 5 10
−14
for moderate values of
x
and
a
(except close to the zeros), while for large
x
and
a
the error is dominated by exponential and trigonometric function evaluations. For IEEE standard double precision arithmetic, the accuracy is better than 5 10
−13
in the computable range of unscaled PCFs (except close to the zeros).
Using MEMS-based storage in computer systems---MEMS storage architectures
Authors: Hong Bo , Wang Feng , Brandt Scott A. , Long Darrell D. E. , Schwarz Thomas J. E.
Published: July 2006

As an emerging nonvolatile secondary storage technology, MEMS-based storage exhibits several desirable properties including high performance, high storage volumic density, low power consumption, low entry cost, and small form factor. However, MEMS-based storage provides a limited amount of storage per device and is likely to be more expensive than magnetic disk. Systems designers will therefore need to make trade-offs to achieve well-balanced designs. We present an architecture in which MEMS devices are organized into MEMS storage enclosures with online spares. Such enclosures are proven to be highly reliable storage building bricks with no maintenance during their economic lifetimes. We also demonstrate the effectiveness of using MEMS as another layer in the storage hierarchy, bridging the cost and performance gap between MEMS storage and disk. We show that using MEMS as a disk cache can significantly improve system performance and cost-performance ratio.
The ugly web
Authors: Weiss Aaron
Published: July 2006

It's remarkable to think that the Web has been here long enough to allow certain trends to start repeating themselves. The personal home pages of 1994 were then derided as hollow vanity projects; the same was said of blogs in 2004. There's a new generation of Web natives, raised on the Internet, now suffering through conversations that begin with "When I was your age, browsing was what we did at shopping malls…" This exchange suggests two inescapable facts: One, we can learn something about the Web's future from its past, and two, those of us saying such things are getting old.
Distributed weighted-multidimensional scaling for node localization in sensor networks
Authors: Costa Jose A. , Patwari Neal , Hero Alfred O.
Published: July 2006

Accurate, distributed localization algorithms are needed for a wide variety of wireless sensor network applications. This article introduces a scalable, distributed weighted-multidimensional scaling (dwMDS) algorithm that adaptively emphasizes the most accurate range measurements and naturally accounts for communication constraints within the sensor network. Each node adaptively chooses a neighborhood of sensors, updates its position estimate by minimizing a local cost function and then passes this update to neighboring sensors. Derived bounds on communication requirements provide insight on the energy efficiency of the proposed distributed method versus a centralized approach. For received signal-strength (RSS) based range measurements, we demonstrate via simulation that location estimates are nearly unbiased with variance close to the Cramér-Rao lower bound. Further, RSS and time-of-arrival (TOA) channel measurements are used to demonstrate performance as good as the centralized maximum-likelihood estimator (MLE) in a real-world sensor network.
Automatic expansion of domain-specific lexicons by term categorization
Authors: Avancini Henri , Lavelli Alberto , Sebastiani Fabrizio , Zanoli Roberto
Published: July 2006

We discuss an approach to the automatic expansion of
domain-specific lexicons
, that is, to the problem of
extending, for each
c

i

in a predefined set
C
=
{
c
1
,…,
c

m

} of
semantic
domains
, an initial lexicon
L

i

0
into a larger lexicon
L

i

1
. Our approach relies on
term categorization
, defined as the task of labeling
previously unlabeled terms according to a predefined set of
domains. We approach this as a supervised learning problem in which
term classifiers are built using the initial lexicons as training
data. Dually to classic text categorization tasks in which
documents are represented as vectors in a space of terms, we
represent terms as vectors in a space of documents. We present the
results of a number of experiments in which we use a boosting-based
learning device for training our term classifiers. We test the
effectiveness of our method by using WordNetDomains, a well-known
large set of domain-specific lexicons, as a benchmark. Our
experiments are performed using the documents in the Reuters Corpus
Volume 1 as implicit representations for our terms.
Adaptive pull-based policies for wide area data delivery
Authors: Bright Laura , Gal Avigdor , Raschid Louiqa
Published: July 2006

Wide area data delivery requires timely propagation of up-to-date information to thousands of clients over a wide area network. Applications include web caching, RSS source monitoring, and email access via a mobile network. Data sources vary widely in their update patterns and may experience different update rates at different times or unexpected changes to update patterns. Traditional data delivery solutions are either push-based, which requires servers to push updates to clients, or pull-based, which require clients to check for updates at servers. While push-based solutions ensure timely data delivery, they are not always feasible to implement and may not scale to a large number of clients. In this article, we present adaptive pull-based policies that explicitly aim to reduce the overhead of contacting remote servers, compared to existing pull-based policies, while meeting freshness requirements. We model updates to data sources using update histories, and present two novel history-based policies to estimate when updates occur; they are based on individual history and aggregate history. These policies are presented within an architectural framework that supports their deployment either client-side or server-side. We further develop two adaptive policies to handle objects that initially may have insufficient history or objects that experience changes in update patterns. Extensive experimental evaluation using three data traces from diverse applications shows that history-based policies can reduce contact between clients and servers by up to 60% compared to existing pull-based policies while providing a comparable level of data freshness. Our experiments further demonstrate that our adaptive policies can select the best policy to match the behavior of an object and perform better than any individual policy, thus they dominate standalone policies.
Solution space navigation for geometric constraint systems
Authors: Sitharam Meera , Arbree Adam , Zhou Yong , Kohareswaran Naganandhini
Published: July 2006

We study the well documented problem of systematically navigating the potentially exponentially many roots or realizations of well-constrained, variational geometric constraint systems. We give a scalable method called the Equation and Solution Manager (ESM) that can be used both for automatic searches and visual, user-driven searches for desired realizations. The method incrementally assembles the desired solution of the entire system and avoids combinatorial explosion by offering the user a visual walk-through of the solutions to recursively constructed subsystems and by permitting the user to make gradual, adaptive solution choices.We isolate requirements on companion methods that are essential and desirable for efficient, meaningful solution space navigation. Specifically, they permit (a) incorporation of many existing approaches to solution space steering or navigation into the ESM; and (b) integration of the ESM into a standard geometric constraint solver architecture. We address the latter challenge and explain how the integration is achieved. Additionally, we sketch the ESM implementation as part of an opensource, 2D and 3D geometric constraint solver, FRONTIER.
Animation planning for virtual characters cooperation
Authors: Esteves Claudia , Arechavaleta Gustavo , Pettré Julien , Laumond Jean-Paul
Published: July 2006

This paper presents an approach to automatically compute animations for virtual (human-like and robot) characters cooperating to move bulky objects in cluttered environments. The main challenge is to deal with 3D collision avoidance while preserving the believability of the agent's behaviors. To accomplish the coordinated task, a geometric and kinematic decoupling of the system is proposed. This decomposition enables us to plan a collision-free path for a reduced system, then to animate locomotion and grasping behaviors independently, and finally to automatically tune the animation to avoid residual collisions. These three steps are applied consecutively to synthesize an animation. The different techniques used, such as probabilistic path planning, locomotion controllers, inverse kinematics and path planning for closed kinematic chains are explained, and the way to integrate them into a single scheme is described.
Intrinsic subdivision with smooth limits for graphics and animation
Authors: Wallner Johannes , Pottmann Helmut
Published: July 2006

This article demonstrates the definition of subdivision processes in nonlinear geometries such that smoothness of limits can be proved. We deal with curve subdivision in the presence of obstacles, in surfaces, in Riemannian manifolds, and in the Euclidean motion group. We show how to model kinematic surfaces and motions in the presence of obstacles via subdivision. As to numerics, we consider the sensitivity of the limit's smoothness to sloppy computing.
Forward rasterization
Authors: Popescu Voicu , Rosen Paul
Published: July 2006

We describe forward rasterization, a class of rendering algorithms designed for small polygonal primitives. The primitive is efficiently rasterized by interpolation between its vertices. The interpolation factors are chosen to guarantee that each pixel covered by the primitive receives at least one sample which avoids holes. The location of the samples is recorded with subpixel accuracy using a pair of offsets which are then used to reconstruct/resample the output image. Offset reconstruction has good static and temporal antialiasing properties. We present two forward rasterization algorithms, one that renders quadrilaterals and is suitable for scenes modeled with depth images like in image-based rendering by 3D warping, and one that renders triangles and is suitable for scenes modeled conventionally. When compared to conventional rasterization, forward rasterization is more efficient for small primitives and has better temporal antialiasing properties.
Discrete conformal mappings via circle patterns
Authors: Kharevych Liliya , Springborn Boris , Schröder Peter
Published: July 2006

We introduce a novel method for the construction of discrete conformal mappings from surface meshes of arbitrary topology to the plane. Our approach is based on
circle patterns
, that is, arrangements of circles---one for each face---with prescribed intersection angles. Given these angles, the circle radii follow as the unique minimizer of a convex energy. The method supports very flexible boundary conditions ranging from free boundaries to control of the boundary shape via prescribed curvatures. Closed meshes of genus zero can be parameterized over the sphere. To parameterize higher genus meshes, we introduce cone singularities at designated vertices. The parameter domain is then a piecewise Euclidean surface. Cone singularities can also help to reduce the often very large area distortion of global conformal maps to moderate levels. Our method involves two optimization problems: a quadratic program and the unconstrained minimization of the circle pattern energy. The latter is a convex function of logarithmic radius variables with simple explicit expressions for gradient and Hessian. We demonstrate the versatility and performance of our algorithm with a variety of examples.
Automated container transport system between inland port and terminals
Authors: Zhang Jianlong , Ioannou Petros A. , Chassiakos Anastasios
Published: July 2006

In this article we propose a new concept called automated container transportation system between inland port and terminals (ACTIPOT) which involves the use of automated trucks to transfer containers between an inland port and container terminals. The inland port is located a few miles away from the terminals and is used for storing and processing import/export containers before distribution to customers or transfer to the terminals. We design and analyze the ACTIPOT system with particular attention paid to the overall supervisory controller that synchronizes all the operations inside the ACTIPOT system. We employ the technique of truck platooning in order to simplify the control of the overall system and to minimize the possibility of deadlocks, congestion, and failures. A microscopic simulation model is developed and used to demonstrate the overall performance of the ACTIPOT system. The contribution of this article is the design, analysis, and evaluation of the new concept ACTIPOT.
A discrete event method for wave simulation
Authors: Nutaro James
Published: July 2006

This article describes a discrete event interpretation of the finite difference time domain (FDTD) and digital wave guide network (DWN) wave simulation schemes. The discrete event method is formalized using the discrete event system specification (DEVS). The scheme is shown to have errors that are proportional to the resolution of the spatial grid. A numerical example demonstrates the relative efficiency of the scheme with respect to FDTD and DWN schemes. The potential for the discrete event scheme to reduce numerical dispersion and attenuation errors is discussed.
Assisting novice analysts in developing quality conceptual models with UML
Authors: Bolloju Narasimha , Leung Felix S.K.
Published: July 2006

Knowing the kinds of modeling errors they are most likely to produce helps prepare novice analysts for developing quality conceptual models.
An efficient overloaded implementation of forward mode automatic differentiation in MATLAB
Authors: Forth Shaun A.
Published: July 2006

The Mad package described here facilitates the evaluation of first derivatives of multidimensional functions that are defined by computer codes written in MATLAB. The underlying algorithm is the well-known forward mode of automatic differentiation implemented via operator overloading on variables of the class fmad. The main distinguishing feature of this MATLAB implementation is the separation of the linear combination of derivative vectors into a separate derivative vector class derivvec. This allows for the straightforward performance optimization of the overall package. Additionally, by internally using a matrix (two-dimensional) representation of arbitrary dimension directional derivatives, we may utilize MATLAB's sparse matrix class to propagate sparse directional derivatives for MATLAB code which uses arbitrary dimension arrays. On several examples, the package is shown to be more efficient than Verma's ADMAT package [Verma 1998a].
A Matlab package for automatically generating Runge-Kutta trees, order conditions, and truncation error coefficients
Authors: Cameron Frank
Published: July 2006

In designing parts of Runge-Kutta methods, order conditions and truncation error coefficients (TECs) are needed. Order conditions and TECs are typically presented as a set of trees combined with rules for producing algebraic expressions from the trees. The tree sets are defined recursively and can be generated by hand only for low orders. This article describes a package of Matlab routines for automatically generating Runge-Kutta trees, order conditions, and TECs. The routines are capable of generating Maple code, Matlab code, or LaTeX expressions for ODEs or DAEs of index 1 and 2. In producing the package, two theoretical problems are tackled: (a) avoiding the repeated generation of the same tree and (b) the efficient storage of TECs.
A spatial data structure for fast Poisson-disk sample generation
Authors: Dunbar Daniel , Humphreys Greg
Published: July 2006

Sampling distributions with blue noise characteristics are widely used in computer graphics. Although Poisson-disk distributions are known to have excellent blue noise characteristics, they are generally regarded as too computationally expensive to generate in real time. We present a new method for sampling by dart-throwing in
O(N
log
N
) time and introduce a novel and efficient variation for generating Poisson-disk distributions in
O(N)
time and space.
Interactive decal compositing with discrete exponential maps
Authors: Schmidt Ryan , Grimm Cindy , Wyvill Brian
Published: July 2006

A method is described for texturing surfaces using
decals
, images placed on the surface using local parameterizations. Decal parameterizations are generated with a novel
O
(
N
log
N
) discrete approximation to the exponential map which requires only a single additional step in Dijkstra's graph-distance algorithm. Decals are dynamically composited in an interface that addresses many limitations of previous work. Tools for image processing, deformation/feature-matching, and vector graphics are implemented using direct surface interaction. Exponential map decals can contain holes and can also be combined with conformal parameterization to reduce distortion. The exponential map approximation can be computed on any point set, including meshes and sampled implicit surfaces, and is relatively stable under resampling. The decals stick to the surface as it is interactively deformed, allowing the texture to be preserved even if the surface changes topology. These properties make exponential map decals a suitable approach for texturing animated implicit surfaces.
Procedural modeling of buildings
Authors: Müller Pascal , Wonka Peter , Haegler Simon , Ulmer Andreas , Van Gool Luc
Published: July 2006

CGA shape
, a novel shape grammar for the procedural modeling of CG architecture, produces building shells with high visual quality and geometric detail. It produces extensive architectural models for computer games and movies, at low cost. Context sensitive shape rules allow the user to specify interactions between the entities of the hierarchical shape descriptions. Selected examples demonstrate solutions to previously unsolved modeling problems, especially to consistent mass modeling with volumetric shapes of arbitrary orientation.
CGA shape
is shown to efficiently generate massive urban models with unprecedented level of detail, with the virtual rebuilding of the archaeological site of Pompeii as a case in point.
Real-time GPU rendering of piecewise algebraic surfaces
Authors: Loop Charles , Blinn Jim
Published: July 2006

We consider the problem of real-time GPU rendering of algebraic surfaces defined by Bézier tetrahedra. These surfaces are rendered directly in terms of their polynomial representations, as opposed to a collection of approximating triangles, thereby eliminating tessellation artifacts and reducing memory usage. A key step in such algorithms is the computation of univariate polynomial coefficients at each pixel; real roots of this polynomial correspond to possibly visible points on the surface. Our approach leverages the strengths of GPU computation and is highly efficient. Furthermore, we compute these coefficients in Bernstein form to maximize the stability of root finding, and to provide shader instances with an early exit test based on the sign of these coefficients. Solving for roots is done using analytic techniques that map well to a SIMD architecture, but limits us to fourth order algebraic surfaces. The general framework could be extended to higher order with numerical root finding.
Appearance manifolds for modeling time-variant appearance of materials
Authors: Wang Jiaping , Tong Xin , Lin Stephen , Pan Minghao , Wang Chao , Bao Hujun , Guo Baining , Shum Heung-Yeung
Published: July 2006

We present a visual simulation technique called
appearance manifolds
for modeling the time-variant surface appearance of a material from data captured at a single instant in time. In modeling time-variant appearance, our method takes advantage of the key observation that concurrent variations in appearance over a surface represent different degrees of weathering. By reorganizing these various appearances in a manner that reveals their relative order with respect to weathering degree, our method infers spatial and temporal appearance properties of the material's weathering process that can be used to convincingly generate its weathered appearance at different points in time. Results with natural non-linear reflectance variations are demonstrated in applications such as visual simulation of weathering on 3D models, increasing and decreasing the weathering of real objects, and material transfer with weathering effects.
Time-varying surface appearance
Authors: Gu Jinwei , Tu Chien-I , Ramamoorthi Ravi , Belhumeur Peter , Matusik Wojciech , Nayar Shree
Published: July 2006

For computer graphics rendering, we generally assume that the appearance of surfaces remains static over time. Yet, there are a number of natural processes that cause surface appearance to vary dramatically, such as burning of wood, wetting and drying of rock and fabric, decay of fruit skins, and corrosion and rusting of steel and copper. In this paper, we take a significant step towards measuring, modeling, and rendering time-varying surface appearance. We describe the acquisition of the first time-varying database of 26 samples, encompassing a variety of natural processes including burning, drying, decay, and corrosion. Our main technical contribution is a Space-Time Appearance Factorization (STAF). This model factors space and time-varying effects. We derive an overall temporal appearance variation characteristic curve of the specific process, as well as space-dependent textures, rates, and offsets. This overall temporal curve controls different spatial locations evolve at the different rates, causing spatial patterns on the surface over time. We show that the model accurately represents a variety of phenomena. Moreover, it enables a number of novel rendering applications, such as transfer of the time-varying effect to a new static surface, control to accelerate time evolution in certain areas, extrapolation beyond the acquired sequence, and texture synthesis of time-varying appearance.
Natural video matting using camera arrays
Authors: Joshi Neel , Matusik Wojciech , Avidan Shai
Published: July 2006

We present an algorithm and a system for high-quality natural video matting using a camera array. The system uses high frequencies present in natural scenes to compute mattes by creating a synthetic aperture image that is focused on the foreground object, which reduces the variance of pixels reprojected from the foreground while increasing the variance of pixels reprojected from the background. We modify the standard matting equation to work directly with variance measurements and show how these statistics can be used to construct a trimap that is later upgraded to an alpha matte. The entire process is completely automatic, including an automatic method for focusing the synthetic aperture image on the foreground object and an automatic method to compute the trimap and the alpha matte. The proposed algorithm is very efficient and has a per-pixel running time that is linear in the number of cameras. Our current system runs at several frames per second, and we believe that it is the first system capable of computing high-quality alpha mattes at near real-time rates without the use of active illumination or special backgrounds.
Fluid animation with dynamic meshes
Authors: Klingner Bryan M. , Feldman Bryan E. , Chentanez Nuttapong , O'Brien James F.
Published: July 2006

This paper presents a method for animating fluid using unstructured tetrahedral meshes that change at each time step. We show that meshes that conform well to changing boundaries and that focus computation in the visually important parts of the domain can be generated quickly and reliably using existing techniques. We also describe a new approach to two-way coupling of fluid and rigid bodies that, while general, benefits from remeshing. Overall, the method provides a flexible environment for creating complex scenes involving fluid animation.
Photo tourism
Authors: Snavely Noah , Seitz Steven M. , Szeliski Richard
Published: July 2006

We present a system for interactively browsing and exploring large unstructured collections of photographs of a scene using a novel 3D interface. Our system consists of an image-based modeling front end that automatically computes the viewpoint of each photograph as well as a sparse 3D model of the scene and image to model correspondences. Our
photo explorer
uses image-based rendering techniques to smoothly transition between photographs, while also enabling full 3D navigation and exploration of the set of images and world geometry, along with auxiliary information such as overhead maps. Our system also makes it easy to construct photo tours of scenic or historic locations, and to annotate image details, which are automatically transferred to other relevant images. We demonstrate our system on several large personal photo collections as well as images gathered from Internet photo sharing sites.
Compression of motion capture databases
Authors: Arikan Okan
Published: July 2006

We present a lossy compression algorithm for large databases of motion capture data. We approximate short clips of motion using Bezier curves and clustered principal component analysis. This approximation has a smoothing effect on the motion. Contacts with the environment (such as foot strikes) have important detail that needs to be maintained. We compress these environmental contacts using a separate, JPEG like compression algorithm and ensure these contacts are maintained during decompression.Our method can compress 6 hours 34 minutes of human motion capture from 1080 MB data into 35.5 MB with little visible degradation. Compression and decompression is fast: our research implementation can decompress at about 1.2 milliseconds/frame, 7 times faster than real-time (for 120 frames per second animation). Our method also yields smaller compressed representation for the same error or produces smaller error for the same compressed size.