bluuebunny/crossref_metadata_2025 huggingface dataset:
Capturing and animating occluded cloth
Authors: White Ryan , Crane Keenan , Forsyth D. A.
Published: September 2007

We capture the shape of moving cloth using a custom set of color markers printed on the surface of the cloth. The output is a sequence of triangle meshes with static connectivity and with detail at the scale of individual markers in both smooth and folded regions. We compute markers' coordinates in space using correspondence across multiple synchronized video cameras. Correspondence is determined from color information in small neighborhoods and refined using a novel strain pruning process. Final correspondence does not require neighborhood information. We use a novel data driven hole-filling technique to fill occluded regions. Our results include several challenging examples: a wrinkled shirt sleeve, a dancing pair of pants, and a rag tossed onto a cup. Finally, we demonstrate that cloth capture is reusable by animating a pair of pants using human motion capture data.
Do HDR displays support LDR content?
Authors: Akyüz Ahmet Oǧuz , Fleming Roland , Riecke Bernhard E. , Reinhard Erik , Bülthoff Heinrich H.
Published: September 2007

The development of high dynamic range (HDR) imagery has brought us to the verge of arguably the largest change in image display technologies since the transition from black-and-white to color television. Novel capture and display hardware will soon enable consumers to enjoy the HDR experience in their own homes. The question remains, however, of what to do with existing images and movies, which are intrinsically low dynamic range (LDR). Can this enormous volume of legacy content also be displayed effectively on HDR displays? We have carried out a series of rigorous psychophysical investigations to determine how LDR images are best displayed on a state-of-the-art HDR monitor, and to identify which stages of the HDR imaging pipeline are perceptually most critical. Our main findings are: (1) As expected, HDR displays outperform LDR ones. (2) Surprisingly, HDR images that are tone-mapped for display on standard monitors are often no better than the best single LDR exposure from a bracketed sequence. (3) Most importantly of all, LDR data does not necessarily require sophisticated treatment to produce a compelling HDR experience. Simply boosting the range of an LDR image linearly to fit the HDR display can equal or even surpass the appearance of a true HDR image. Thus the potentially tricky process of
inverse tone mapping
can be largely circumvented.
FiberMesh
Authors: Nealen Andrew , Igarashi Takeo , Sorkine Olga , Alexa Marc
Published: September 2007

This paper presents a system for designing freeform surfaces with a collection of 3D curves. The user first creates a rough 3D model by using a sketching interface. Unlike previous sketching systems, the user-drawn strokes stay on the model surface and serve as handles for controlling the geometry. The user can add, remove, and deform these control curves easily, as if working with a 2D line drawing. The curves can have arbitrary topology; they need not be connected to each other. For a given set of curves, the system automatically constructs a smooth surface embedding by applying functional optimization. Our system provides real-time algorithms for both control curve deformation and the subsequent surface optimization. We show that one can create sophisticated models using this system, which have not yet been seen in previous sketching or functional optimization systems.
Interactive editing and modeling of bidirectional texture functions
Authors: Kautz Jan , Boulos Solomon , Durand Frédo
Published: September 2007

While measured Bidirectional Texture Functions (BTF) enable impressive realism in material appearance, they offer little control, which limits their use for content creation. In this work, we interactively manipulate BTFs and create new BTFs from flat textures. We present an out-of-core approach to manage the size of BTFs and introduce new editing operations that modify the appearance of a material. These tools achieve their full potential when selectively applied to subsets of the BTF through the use of new selection operators. We further analyze the use of our editing operators for the modification of important visual characteristics such as highlights, roughness, and fuzziness. Results compare favorably to the direct alteration of micro-geometry and reflectances of synthetic reference data.
AppWand
Authors: Pellacini Fabio , Lawrence Jason
Published: September 2007

We investigate a new approach to editing spatially- and temporally-varying measured materials that adopts a stroke-based workflow. In our system, a user specifies a small number of editing constraints with a 3-D painting interface which are smoothly propagated to the entire dataset through an optimization that enforces similar edits are applied to areas with similar appearance. The sparse nature of this
appearance-driven
optimization permits the use of efficient solvers, allowing the designer to interactively refine the constraints. We have found this approach supports specifying a wide range of complex edits that would not be easy with existing techniques which present the user with a fixed segmentation of the data. Furthermore, it is independent of the underlying reflectance model and we show edits to both analytic and non-parametric representations in examples from several material databases.
Isosurface stuffing
Authors: Labelle François , Shewchuk Jonathan Richard
Published: September 2007

The
isosurface stuffing
algorithm fills an isosurface with a uniformly sized tetrahedral mesh whose dihedral angles are bounded between 10.7° and 164.8°, or (with a change in parameters) between 8.9° and 158.8°. The algorithm is whip fast, numerically robust, and easy to implement because, like Marching Cubes, it generates tetrahedra from a small set of precomputed stencils. A variant of the algorithm creates a mesh with internal grading: on the boundary, where high resolution is generally desired, the elements are fine and uniformly sized, and in the interior they may be coarser and vary in size. This combination of features makes isosurface stuffing a powerful tool for dynamic fluid simulation, large-deformation mechanics, and applications that require interactive remeshing or use objects defined by smooth implicit surfaces. It is the first algorithm that rigorously guarantees the suitability of tetrahedra for finite element methods in domains whose shapes are substantially more challenging than boxes. Our angle bounds are guaranteed by a computer-assisted proof. If the isosurface is a smooth 2-manifold with bounded curvature, and the tetrahedra are sufficiently small, then the boundary of the mesh is guaranteed to be a geometrically and topologically accurate approximation of the isosurface.
Geometric modeling in shape space
Authors: Kilian Martin , Mitra Niloy J. , Pottmann Helmut
Published: September 2007

We present a novel framework to treat shapes in the setting of Riemannian geometry. Shapes -- triangular meshes or more generally straight line graphs in Euclidean space -- are treated as points in a shape space. We introduce useful Riemannian metrics in this space to aid the user in design and modeling tasks, especially to explore the space of (approximately) isometric deformations of a given shape. Much of the work relies on an efficient algorithm to compute geodesics in shape spaces; to this end, we present a multi-resolution framework to solve the interpolation problem -- which amounts to solving a boundary value problem -- as well as the extrapolation problem -- an initial value problem -- in shape space. Based on these two operations, several classical concepts like parallel transport and the exponential map can be used in shape space to solve various geometric modeling and geometry processing tasks. Applications include shape morphing, shape deformation, deformation transfer, and intuitive shape exploration.
Real-time enveloping with rotational regression
Authors: Wang Robert Y. , Pulli Kari , Popović Jovan
Published: September 2007

Enveloping, or the mapping of skeletal controls to the deformations of a surface, is key to driving realistic animated characters. Despite its widespread use, enveloping still relies on slow or inaccurate deformation methods. We propose a method that is both fast, accurate and example-based. Our technique introduces a rotational regression model that captures common skinning deformations such as muscle bulging, twisting, and challenging areas such as the shoulders. Our improved treatment of rotational quantities is made practical by model reduction that ensures real-time solution of least-squares problems, independent of the mesh size. Our method is significantly more accurate than linear blend skinning and almost as fast, suggesting its use as a replacement for linear blend skinning when examples are available.
Color images visible under UV light
Authors: Hersch Roger D. , Donzé Philipp , Chosson Sylvain
Published: September 2007

The present contribution aims at creating color images printed with fluorescent inks that are only visible under UV light. The considered fluorescent inks absorb light in the UV wavelength range and reemit part of it in the visible wavelength range. In contrast to normal color printing which relies on the spectral absorption of light by the inks, at low concentration fluorescent inks behave additively, i.e. their light emission spectra sum up. We first analyze to which extent different fluorescent inks can be superposed. Due to the quenching effect, at high concentrations of the fluorescent molecules, the fluorescent effect diminishes. With an ink-jet printer capable of printing pixels at reduced dot sizes, we reduce the concentration of the individual fluorescent inks and are able to create from the blue, red and greenish-yellow inks the new colorants white and magenta. In order to avoid quenching effects, we propose a color halftoning method relying on diagonally oriented pre-computed screen dots, which are printed side by side. For gamut mapping and color separation, we create a 3D representation of the fluorescent ink gamut in CIELAB space by predicting halftone fluorescent emission spectra according to the spectral Neugebauer model. Thanks to gamut mapping and juxtaposed halftoning, we create color images, which are invisible under daylight and have, under UV light, a high resemblance with the original images.
Stochastic simplification of aggregate detail
Authors: Cook Robert L. , Halstead John , Planck Maxwell , Ryu David
Published: September 2007

Many renderers perform poorly on scenes that contain a lot of detailed geometry. The load on the renderer can be alleviated by simplification techniques, which create less expensive representations of geometry that is small on the screen. Current simplification techniques for high-quality surface-based rendering tend to work best with element detail (i.e., detail due to the complexity of individual elements) but not as well with aggregate detail (i.e., detail due to the large number of elements). To address this latter type of detail, we introduce a stochastic technique related to some approaches used for point-based renderers. Scenes are rendered by randomly selecting a subset of the geometric elements and altering those elements statistically to preserve the overall appearance of the scene. The amount of simplification can depend on a number of factors, including screen size, motion blur, and depth of field.
Image-based tree modeling
Authors: Tan Ping , Zeng Gang , Wang Jingdong , Kang Sing Bing , Quan Long
Published: September 2007

In this paper, we propose an approach for generating 3D models of natural-looking trees from images that has the additional benefit of requiring little user intervention. While our approach is primarily image-based, we do not model each leaf directly from images due to the large leaf count, small image footprint, and widespread occlusions. Instead, we populate the tree with leaf replicas from segmented source images to reconstruct the overall tree shape. In addition, we use the shape patterns of visible branches to predict those of obscured branches. We demonstrate our approach on a variety of trees.
Approximate image-based tree-modeling using particle flows
Authors: Neubert Boris , Franken Thomas , Deussen Oliver
Published: September 2007

We present a method for producing 3D tree models from input photographs with only limited user intervention. An approximate voxel-based tree volume is estimated using image information. The density values of the voxels are used to produce initial positions for a set of particles. Performing a 3D flow simulation, the particles are traced downwards to the tree basis and are combined to form twigs and branches. If possible, the trunk and the first-order branches are determined in the input photographs and are used as attractors for particle simulation. The geometry of the tree skeleton is produced using botanical rules for branch thicknesses and branching angles. Finally, leaves are added. Different initial seeds for particle simulation lead to a variety, yet similar-looking branching structures for a single set of photographs.
Fast triangle reordering for vertex locality and reduced overdraw
Authors: Sander Pedro V. , Nehab Diego , Barczak Joshua
Published: September 2007

We present novel algorithms that optimize the order in which triangles are rendered, to improve post-transform vertex cache efficiency as well as for view-independent overdraw reduction. The resulting triangle orders perform on par with previous methods, but are orders magnitude faster to compute.

The improvements in processing speed allow us to perform the optimization right after a model is loaded, when more information on the host hardware is available. This allows our vertex cache optimization to often outperform other methods. In fact, our algorithms can even be executed interactively, allowing for re-optimization in case of changes to geometry or topology, which happen often in CAD/CAM applications. We believe that most real-time rendering applications will immediately benefit from these new results.
A hardware architecture for surface splatting
Authors: Weyrich Tim , Heinzle Simon , Aila Timo , Fasnacht Daniel B. , Oetiker Stephan , Botsch Mario , Flaig Cyril , Mall Simon , Rohrer Kaspar , Felber Norbert , Kaeslin Hubert , Gross Markus
Published: September 2007

We present a novel architecture for hardware-accelerated rendering of point primitives. Our pipeline implements a refined version of EWA splatting, a high quality method for antialiased rendering of point sampled representations. A central feature of our design is the seamless integration of the architecture into conventional, OpenGL-like graphics pipelines so as to complement triangle-based rendering. The specific properties of the EWA algorithm required a variety of novel design concepts including a ternary depth test and using an on-chip pipelined heap data structure for making the memory accesses of splat primitives more coherent. In addition, we developed a computationally stable evaluation scheme for perspectively corrected splats. We implemented our architecture both on reconfigurable FPGA boards and as an ASIC prototype, and we integrated it into an OpenGL-like software implementation. Our evaluation comprises a detailed performance analysis using scenes of varying complexity.
Efficient gradient-domain compositing using quadtrees
Authors: Agarwala Aseem
Published: September 2007

We describe a hierarchical approach to improving the efficiency of
gradient-domain compositing
, a technique that constructs seamless composites by combining the gradients of images into a vector field that is then integrated to form a composite. While gradient-domain compositing is powerful and widely used, it suffers from poor scalability. Computing an
n
pixel composite requires solving a linear system with
n
variables; solving such a large system quickly overwhelms the main memory of a standard computer when performed for multi-megapixel composites, which are common in practice. In this paper we show how to perform gradient-domain compositing approximately by solving an
O(p)
linear system, where
p
is the total length of the seams between image regions in the composite; for typical cases,
p
is
O
(√
n
). We achieve this reduction by transforming the problem into a space where much of the solution is smooth, and then utilize the pattern of this smoothness to adaptively subdivide the problem domain using quadtrees. We demonstrate the merits of our approach by performing panoramic stitching and image region copy-and-paste in significantly reduced time and memory while achieving visually identical results.
Video watercolorization using bidirectional texture advection
Authors: Bousseau Adrien , Neyret Fabrice , Thollot Joëlle , Salesin David
Published: September 2007

In this paper, we present a method for creating watercolor-like animation, starting from video as input. The method involves two main steps: applying textures that simulate a watercolor appearance; and creating a simplified, abstracted version of the video to which the texturing operations are applied. Both of these steps are subject to highly visible temporal artifacts, so the primary technical contributions of the paper are extensions of previous methods for texturing and abstraction to provide temporal coherence when applied to video sequences. To maintain coherence for textures, we employ texture advection along lines of optical flow. We furthermore extend previous approaches by incorporating advection in both forward and reverse directions through the video, which allows for minimal texture distortion, particularly in areas of disocclusion that are otherwise highly problematic. To maintain coherence for abstraction, we employ mathematical morphology extended to the temporal domain, using filters whose temporal extents are locally controlled by the degree of distortions in the optical flow. Together, these techniques provide the first practical and robust approach for producing watercolor animations from video, which we demonstrate with a number of examples.
Offshore outsourcing
Authors: Ramingwong Sakgasit , Sajeev A. S. M.
Published: September 2007

Breaking the code of silence.
An investigation into web accessibility standards as a practical study with older and disabled citizens
Authors: Bevan Thomas , Ahmed Amr
Published: September 2007

To coincide with the growth of online services, website standards are progressing to evolve to maintain levels of consistency and usability amongst all web design. Another important aspect is also to include as many users and user groups as possible, especially older and disabled users, given the high potential benefits for those users from the online information, advices, and services. The changes brought about by standardising web design can be both large and small. Ideally the changes will be small enough to go unnoticed by users, but our aim was to see whether even the small changes can make reasonable differences for test users.
Accessibility research at the department of mechatronics at Darmstadt University of Technology
Authors: Felzer Torsten , Ernst Martin , Strah Bruno , Nordmann Rainer
Published: September 2007

Before the first author joined the department, the research group around Prof. Nordmann exclusively focused on 'classic' Mechatronics issues, such as
active magnetic bearings and squeeze film dampers
. This changed in 2004, when the first author -- who had developed a hands-free control system for an electric wheelchair within the framework of his PhD thesis (see [1]) -- became an active part of the group.
From the editors
Authors: Stafford Tom , Chau Patrick Y. K.
Published: September 2007

Greetings from the Editorial Suite! Big things are going on here at your Data Base.

We've completely settled in to our new online manuscript review portal, which you can find linked at our site (http://the-database.org) or directly accessed through http://www.editorialmanager.com/sigmisdb/. Try it; you'll like it. It seems that more and more of the leading journals are going online with their reviewing processes. It makes great sense, and streamlines the process of reviewing and revising manuscripts mightily.

I was reminded by past Editor Detmar Straub that we're actually the oldest mainstream peer-reviewed MIS publication around. Having started life years ago as an in-house publication of the ACM SIGMIS (or, what used to be called "business information technology"), this publication has been through a number of evolutions.

Hang on, we're only getting started! We are just wrapping up our survey with Thomson ISI for cover-age in the Social Sciences Citation Index, we've launched an online portal for managing the review process, we've expanded coverage globally with our Global Co-Editor Patrick Chau in Hong Kong. There's more in the works; stay tuned.

As of this issue we bid adieu and good luck to our friend Denny Kramer, who has been Technical Editor for the publication for years. Denny got an offer he could not refuse (just remember to call him "Dean Kramer" next time you see him) and had to bow out of the Technical Editor duties. As of our next issue, Prof. Clint Lanier of the Center for the Study of Rhetoric and Applied Communication at The University of Memphis takes the reins. Welcome Clint!.

We have some very interesting research themed issues coming soon. The response to the call for papers for the Virtual Worlds issue was extensive; expect something extra-special from that within the year. We have an issue planned from selected top-tier papers from the new AIS conference in China, and we will be welcoming Al Hevner to our pages as Guest Editor for a very special issue on Software Testing, shortly.

Data Base - more than just database research. In fact, you'll find, and we heartily welcome, just about any topic in the area of information systems in our pages. Just as has been the case for years, and years and years. Did I say we're the oldest general MIS publication around?.

We welcome your participation in this fine tradition. Send us your papers at our submission portal, http://www.editorialmanager.com/sigmisdb/.
The tyranny of methodologies in information systems research
1
Authors: Gallupe R. Brent
Published: September 2007

A preoccupation with research methodologies is negatively affecting the quality of information systems (IS) research. Current IS research seems more concerned with "how" the research is conducted rather than "what" research is conducted and "why". This "tyranny of methodologies in IS research" is having a number of effects on IS research including influencing the problems that are chosen for study, affecting the papers that are selected for publication, and generally influencing the direction of the entire field. This paper explores this phenomenon. The paper describes the context and outlines the dimensions of the problem. It compares the "methodologies problem" in the IS field with the use of methodologies in other management disciplines. Finally, it proposes a number of approaches to help the IS discipline take a more balanced perspective in terms of the research methodologies it use.
Visualization of web spaces
Authors: Turetken Ozgur , Sharda Ramesh
Published: September 2007

The World Wide Web is a dominant global communication medium and knowledge repository. It is used by a great number of people with a variety of computer skills hence its usability is critical. As with many large information collections, the challenge with web usability is understanding the structure of a collection of information objects (web pages) to find relevant ones for satisfying a specific information need. Web sites are organized in a hyperlinked structure that somewhat addresses this challenge. However, this "connectedness" also causes the now well-known "lost in cyberspace" phenomenon where one may get confused within the complex organization of a web site. Meanwhile, information exploration on the web is not limited to browsing a web site. The problem of finding relevant information applies to a collection of pages that come from various web sites as in the case of the results of a "less than perfectly constructed" search query.

Information visualization has been proposed as a way to cope with these problems by taking advantage of people's innate perceptual skills to support their cognitive skills. Many paradigms have been proposed for the visual presentation of web spaces (i.e. structured or unstructured collection of web pages). This study surveys these paradigms to provide a map of where the research in this field is, and what directions future research and practice can take. For this, we introduce a classification scheme to help in the systematic understanding of web visualization and for providing a framework for the development of future visualizations.
A layered approach to simplified access control in virtualized systems
Authors: Payne Bryan D. , Sailer Reiner , Cáceres Ramón , Perez Ron , Lee Wenke
Published: September 2007

In this work, we show how the abstraction layer created by a hypervisor, or virtual machine monitor, can be leveraged to reduce the complexity of mandatory access control policies throughout the system. Policies governing access control decisions in today's systems are complex and monolithic. Achieving strong security guarantees often means restricting usability across the entire system, which is a primary reason why mandatory access controls are rarely deployed. Our architecture uses a hypervisor and multiple virtual machines to decompose policies into multiple layers. This simplifies the policies and their enforcement, while minimizing the overall impact of security on the system. We show that the overhead of decomposing system policies into distinct policies for each layer can be negligible. Our initial implementation confirms that such layering leads to simpler security policies and enforcement mechanisms as well as a more robust layered trusted computing base. We hope that this work serves to start a dialog regarding the use of mandatory access controls within a hypervisor for both increasing security and improving manageability.
Responsibilities for funding university computing centers
Authors: Smith Charles
Published: September 2007

Since the theme of the 1971 Spring Joint Computer Conference is "Responsibility", this paper will focus on the responsibility of those involved with use and control of computer technology in colleges and universities to establish a framework for efficient and effective use of this technology on campus.
Abstracts of special session on differential algebra
Authors: Sit William
Published: September 2007

The Special Session on Differential Algebra of the American Mathematical Society (AMS) Eastern Section Spring Meeting, will be held on April 14-15, 2007 at Stevens Institute of Technology, New Jersey, USA. The following abstracts of invited speakers at this Special Session have been edited for reproduction by kind permission of AMS. With some exceptions, they are listed in alphabetical order by presenters. For all abstracts, only the email contact information of the presenter is given. The Special Session is jointly organized by the Kolchin Seminar in Differential Algebra of the City University of New York and the Department of Mathematics and Computer Science at Newark Campus of Rutgers, the State University of New Jersey. For further information, please visit site below.
From myth to mountain
Authors: Rohde Joe
Published: September 2007

Many of us are engaged in one form or another of story-crafting, whether in two dimensional and virtual media, or in the three dimensional world of built environments, in which I work. Common to all of this is the importance of a good foundational basis for creative expression, through the rigorous application of narrative design principles to all aspects of a project.
Application of Dijkstra's weakest precondition calculus to Dining Philosophers problem
Authors: Banerjee Jayasri , Bandyopadhyay Anup Kumar , Mandal Ajit Kumar
Published: September 2007

Dijkstra's weakest precondition calculus is used to model the well known Dining Philosophers problem. Process and state definitions are done in such a manner that only the deadlock property of the system is highlighted. Care has been taken to choose the proper details such that it is not too elaborate to obscure the requirements also not be too abstract to mask the actual analytical needs. State transition rules specify the system behavior. Intuitive reasoning as well as formal technique has been applied to get the deadlock condition. Two well known solutions are specified and proved. The proof technique being analytical, its complexity does not depend on the size of the problem. The second solution requires an event ordering and therefore a temporal ordering predicate has been used to prove its correctness.
Surfing the net for software engineering notes
Authors: Doernhoefer Mark
Published: September 2007

Database programming doesn't provide the excitement of game programming or the instant gratification of a flashy web application, but the ability to store and retrieve information in an organized manner is vital to the operation of many client-server or web-based applications. Construction of a solid application often depends upon a well built database to provide persistent storage of the data needed to power the application. So although database planning and design may be boring, it is a necessary step in the software engineering process.
Realising evidence-based software engineering (REBSE-2) a report from the workshop held at ICSE 2007
Authors: Budgen David , Brereton Pearl
Published: September 2007

Context:
The REBSE international workshops are concerned with exploring the adaptation and use of the evidence-based paradigm in software engineering research and practice, through a mix of presentations and discussion.

Objectives:
These were to explore both experience with, and potential for, evidence-based software engineering (EBSE); to consider how this might affect empirical practices in software engineering; and to work towards creating a community of researchers to practice and promote EBSE.

Method:
Three sessions were dedicated to a mix of presentations and interactive discussion, while the fourth was dedicated to summarising progress and identifying both issues of concern and actions to pursue.

Conclusions:
While we identified a number of issues, a key need is clearly to have a central repository to both provide information and to maintain a record of activity in this area.
Building Secure Web Applications
Authors: Neville-Neil George V.
Published: September 2007

In these days of phishing and near-daily announcements of identity theft via large-scale data losses, it seems almost ridiculous to talk about securing the Web. At this point most people seem ready to throw up their hands at the idea or to lock down one small component that they can control in order to keep the perceived chaos at bay.
Some Swans are Black
Authors: Kelly-Bootle Stan
Published: September 2007

You may well expect from my title that I’m about to plumb the depths of Nassim Nicholas Taleb’s theories on catastrophe and quasi-empirical randomness. I, in turn, expect that you’ve already read Taleb’s best-selling The Black Swan—The Impact of the Highly Improbable dealing with life’s innate uncertainties and how to expect or even cope with the unexpected. Coping involves learning that the right answer to some problems is, “Don’t know.” I was tempted to end my column right here in order to prove something or other about our many failures in predicting the future, compared with our occasional successes in “postdicting” the past.
IEEE 802.21 enabled mobile terminals for optimized WLAN/3G handovers
Authors: de la Oliva Antonio , Melia Telemaco , Vidal Albert , Bernardos Carlos J. , Soto Ignacio , Banchs Albert
Published: September 2007

Wireless LAN hotspots are becoming widely spread. This, combined with the availability of new multi-mode terminals integrating heterogeneous technologies, opens new business opportunities for Mobile Operators. Scenarios in which 3G coverage is complemented by Wireless LAN deployments are becoming available. Therefore all IP based networks are ready to offer a new variety of services across heterogeneous access. However, to achieve this, some aspects still need to be analyzed. In particular, how and when to execute handovers in order to minimize service interruptions and maximize the use of the most appropriate technologies according to user's preferences (for example, a user may prefer to use a lower cost technology if available). This paper presents a simulation study of handover performance between 3G and Wireless LAN access networks. The mobile devices are based on the IEEE 802.21 cross layer architecture and use Wireless LAN signal level thresholds as handover criteria.
On the structure of user association patterns in wireless LANs
Authors: Hsu Wei-jen , Dutta Debojyoti , Helmy Ahmed
Published: September 2007

There has been a rapid increase in wireless LAN (WLAN) deployments, users and traffic in recent years. Thus there is an urgent need to mine the finegrained analysis of the structures and trends in wireless user association patterns. Such study could have significant impact on the design of behavior-aware services and protocols to create social networks based on similar behavioral patterns. In this paper, we propose new methods to understand such trends of user associations in a campus WLAN, and ways of quantifying those trends. Our goal is to quantify repetitive and consistent patterns of user association behavior.
Cross-layer protocol design for delay/fault-tolerant mobile sensor networks
Authors: Wang Yu , Lin Feng , Wu Hongyi
Published: September 2007

Recent development in sensor and networking technologies has made it possible to deploy deeply embedded sensor system for pervasive information gathering. One typical example is flu virus tracking, where the goal is to collect data of flu virus (or any epidemic disease in general), in the area with high human activities in order to monitor and prevent the explosion of devastating flu. Another example is air quality monitoring, which aims to track the average toxic gas inbreathed by human beings everyday.
In search for an appropriate granularity to model routing policies
Authors: Mühlbauer Wolfgang , Uhlig Steve , Fu Bingjie , Meulle Mickael , Maennel Olaf
Published: September 2007

Routing policies are typically partitioned into a few classes that capture the most common practices in use today[1]. Unfortunately, it is known that the reality of routing policies[2] and peering relationships is far more complex than those few classes[1,3]. We take the next step of searching for the appropriate granularity at which policies should be modeled. For this purpose, we study how and where to configure per-prefix policies in an AS-level model of the Internet, such that the selected paths in the model are consistent with those observed in BGP data from multiple vantage points.

By comparing business relationships with per-prefix filters, we investigate the role and limitations of business relationships as a model for policies. We observe that popular locations for filtering correspond to
valleys
where no path should be propagated according to inferred business relationships. This result reinforces the validity of the
valley-free
property used for business relationships inference. However, given the sometimes large path diversity ASs have, business relationships do not contain enough information to decide which path will be chosen as the best. To model how individual ASs choose their best paths, we introduce a new abstraction:
next-hop atoms
. Next-hop atoms capture the different sets of neighboring ASs an AS uses for its best routes. We show that a large fraction of next-hop atoms correspond to per-neighbor path choices. A non-negligible fraction of path choices, however, correspond to hot-potato routing and tie-breaking within the BGP decision process, very detailed aspects of Internet routing.
Resolving inter-domain policy disputes
Authors: Ee Cheng Tien , Ramachandran Vijay , Chun Byung-Gon , Lakshminarayanan Kaushik , Shenker Scott
Published: September 2007

The Border Gateway Protocol (BGP) allows each autonomous system (AS) to select routes to destinations based on semantically rich and locally determined policies. This autonomously exercised policy freedom can cause instability, where unresolvable policy-based disputes in the network result in interdomain route oscillations. Several recent works have established that such instabilities can only be eliminated by enforcing a globally accepted preference ordering on routes (such as shortest path). To resolve this conflict between policy autonomy and system stability, we propose a distributed mechanism that enforces a preference ordering only when disputes resulting in oscillations exist. This preserves policy freedom when possible, and imposes stability when required.
Trading structure for randomness in wireless opportunistic routing
Authors: Chachulski Szymon , Jennings Michael , Katti Sachin , Katabi Dina
Published: September 2007

Opportunistic routing is a recent technique that achieves high throughput in the face of lossy wireless links. The current opportunistic routing protocol, ExOR, ties the MAC with routing, imposing a strict schedule on routers' access to the medium. Although the scheduler delivers opportunistic gains, it misses some of the inherent features of the 802.11 MAC. For example, it prevents spatial reuse and thus may underutilize the wireless medium. It also eliminates the layering abstraction, making the protocol less amenable to extensions to alternate traffic types such as multicast.

This paper presents MORE, a MAC-independent opportunistic routing protocol. MORE randomly mixes packets before forwarding them. This randomness ensures that routers that hear the same transmission do not forward the same packets. Thus, MORE needs no special scheduler to coordinate routers and can run directly on top of 802.11. Experimental results from a 20-node wireless testbed show that MORE's median unicast throughput is 22% higher than ExOR, and the gains rise to 45% over ExOR when there is a chance of spatial reuse. For multicast, MORE's gains increase with the number of destinations, and are 35-200% greater than ExOR.
An axiomatic basis for communication
Authors: Karsten Martin , Keshav S. , Prasad Sanjiva , Beg Mirza
Published: September 2007

The de facto service architecture of today's communication networks, in particular the Internet, is heterogeneous, complex, ad hoc, and not particularly well understood. With layering as the only means for functional abstraction, and even this violated by middle-boxes, the diversity of current technologies can barely be expressed, let alone analyzed. As a first step to remedying this problem, we present an axiomatic formulation of fundamental forwarding mechanisms in communication networks. This formulation allows us to express precisely and abstractly the concepts of
naming
and
addressing
and to specify a consistent set of control patterns and operational primitives, from which a variety of communication services can be composed. Importantly, this framework can be used to (1) formally analyze network protocols based on structural properties, and also to (2) derive working prototype implementations of these protocols. The prototype is implemented as a
universal forwarding engine
, a general framework and runtime environment based on the Click router.
Etherfuse
Authors: Elmeleegy Khaled , Cox Alan L. , Ng T. S. Eugene
Published: September 2007

Ethernet is pervasive. This is due in part to its ease of use. Equipment can be added to an Ethernet network with little or no manual configuration. Furthermore, Ethernet is self-healing in the event of equipment failure or removal. However, there are scenarios where a local event can lead to network-wide packet loss and duplication due to slow or faulty reconfiguration of the spanning tree. Moreover, in some cases the packet loss and duplication may persist indefinitely.

To address these problems, we introduce the EtherFuse, a new device that can be inserted into an existing Ethernet to speed the reconfiguration of the spanning tree and suppress packet duplication. EtherFuse is backward compatible and requires no change to the existing hardware, software, or protocols. We describe a prototype EtherFuse implementation and experimentally demonstrate its effectiveness. Specifically, we characterize how quickly it responds to network failures, its ability to reduce packet loss and duplication, and its benefits on the end-to-end performance of common applications.
A study of prefix hijacking and interception in the internet
Authors: Ballani Hitesh , Francis Paul , Zhang Xinyang
Published: September 2007

There have been many incidents of prefix hijacking in the Internet. The hijacking AS can blackhole the hijacked traffic. Alternatively, it can transparently intercept the hijacked traffic by forwarding it onto the owner. This paper presents a study of such prefix hijacking and interception with the following contributions: (1). We present a methodology for prefix interception, (2). We estimate the fraction of traffic to any prefix that can be hijacked and intercepted in the Internet today, (3). The interception methodology is implemented and used to intercept real traffic to our prefix, (4). We conduct a detailed study to detect ongoing prefix interception.

We find that: Our hijacking estimates are in line with the impact of past hijacking incidents and show that ASes higher up in the routing hierarchy can hijack a significant amount of traffic to any prefix, including popular prefixes. A less apparent result is that the same holds for prefix interception too. Further, our implementation shows that intercepting traffic to a prefix in the Internet is almost as simple as hijacking it. Finally, while we fail to detect ongoing prefix interception, the detection exercise highlights some of the challenges posed by the prefix interception problem.
How dynamic are IP addresses?
Authors: Xie Yinglian , Yu Fang , Achan Kannan , Gillum Eliot , Goldszmidt Moises , Wobber Ted
Published: September 2007

This paper introduces a novel algorithm,
UDmap
, to identify dynamically assigned IP addresses and analyze their dynamics pattern. UDmap is fully automatic, and relies only on application-level server logs. We applied UDmap to a month-long Hotmail user-login trace and identified a significant number of dynamic IP addresses - more than 102 million. This suggests that the fraction of IP addresses that are dynamic is by no means negligible. Using this information in combination with a three-month Hotmail email server log, we were able to establish that 95.6% of mail servers setup on the dynamic IP addresses in our trace sent out solely spam emails. Moreover, these mail servers sent out a large amount of spam - amounting to 42.2% of all spam emails received by Hotmail. These results highlight the importance of being able to accurately identify dynamic IP addresses for spam filtering. We expect similar benefits to arise for phishing site identification and botnet detection. To our knowledge, this is the first successful attempt to automatically identify and understand IP address dynamics.
Cloud control with distributed rate limiting
Authors: Raghavan Barath , Vishwanath Kashi , Ramabhadran Sriram , Yocum Kenneth , Snoeren Alex C.
Published: September 2007

Today's cloud-based services integrate globally distributed resources into seamless computing platforms. Provisioning and accounting for the resource usage of these Internet-scale applications presents a challenging technical problem. This paper presents the design and implementation of distributed rate limiters, which work together to enforce a global rate limit across traffic aggregates at multiple sites, enabling the coordinated policing of a cloud-based service's network traffic. Our abstraction not only enforces a global limit, but also ensures that congestion-responsive transport-layer flows behave as if they traversed a single, shared limiter. We present two designs - one general purpose, and one optimized for TCP - that allow service operators to explicitly trade off between communication costs and system accuracy, efficiency, and scalability. Both designs are capable of rate limiting thousands of flows with negligible overhead (less than 3% in the tested configuration). We demonstrate that our TCP-centric design is scalable to hundreds of nodes while robust to both loss and communication delay, making it practical for deployment in nationwide service providers.
Embracing wireless interference
Authors: Katti Sachin , Gollakota Shyamnath , Katabi Dina
Published: September 2007

Traditionally, interference is considered harmful. Wireless networks strive to avoid scheduling multiple transmissions at the same time in order to prevent interference. This paper adopts the opposite approach; it encourages strategically picked senders to interfere. Instead of forwarding packets, routers forward the interfering signals. The destination leverages network-level information to cancel the interference and recover the signal destined to it. The result is
analog network coding
because it mixes signals not bits.

So, what if wireless routers forward signals instead of packets? Theoretically, such an approach doubles the capacity of the canonical 2-way relay network. Surprisingly, it is also practical. We implement our design using software radios and show that it achieves significantly higher throughput than both traditional wireless routing and prior work on wireless network coding.
What's wrong with online privacy policies?
Authors: Pollach Irene
Published: September 2007

Research has shown that privacy policies tend to intensify privacy concerns rather than engender trust. One way to combat this dichotomy is to redesign their content, language, and presentation format.
Why you can't cite Wikipedia in my class
Authors: Waters Neil L.
Published: September 2007

The online encyclopedia's method of adding information risks conflating facts with popular opinion.
Toward a world with quantum computers
Authors: Bacon Dave , Leung Debbie
Published: September 2007

Surveying the recent past and projecting future developments and applications involving quantum information science.
Exercises and problems
Authors: Polivka Ray
Published: September 2007

The Skyline problem that appeared in the Volume 34, No.4 issue had only three responders. One problem solver was Charles Bovaird. He used APLPC. The other two submitters were Adam Kertesz and myself. Our solutions provide an interesting contrast.
Relativity of Remembering: Why the Laws of Memory Vanished
Authors: Roediger, III Henry L.
Published: September 2007

For 120 years, cognitive psychologists have sought general laws of learning and memory. In this review I conclude that none has stood the test of time. No empirical law withstands manipulation across the four sets of factors that Jenkins (1979) identified as critical to memory experiments: types of subjects, kinds of events to be remembered, manipulation of encoding conditions, and variations in test conditions. Another factor affecting many phenomena is whether a manipulation of conditions occurs in randomized, within-subjects designs rather than between-subjects (or within-subject, blocked) designs. The fact that simple laws do not hold reveals the complex, interactive nature of memory phenomena. Nonetheless, the science of memory is robust, with most findings easily replicated under the same conditions as originally used, but when other variables are manipulated, effects may disappear or reverse. These same points are probably true of psychological research in most, if not all, domains.