bluuebunny/crossref_metadata_2025 huggingface dataset:
Black spruce and jack pine dynamics simulated under varying fire cycles in the northern boreal forest of Quebec, Canada
Authors: Goff Héloïse Le , Sirois Luc
Published: January 2005

The postfire regeneration dynamics of black spruce and jack pine were documented by a study of three successive cohorts (woody debris, snags, seedlings) within a large area burnt in 1989. The objectives of this study were (i) to describe how fire interval can influence the abundance of regenerating black spruce and jack pine and (ii) to model the future abundance trends of these two species for fire cycles of different lengths. The transition probabilities after fire were calculated for mixed stands of black spruce and jack pine for fire intervals of 47 and 67 years in well-drained sites and for fire intervals varying between 92 and 270 years in poorly drained sites. These probabilities were incorporated into a model of regeneration dynamics that took into account the drainage type, the regeneration potential, and the natural mortality rate of both species. After the 1989 fire, jack pine seedlings made up 55%82% of the regeneration in well-drained sites and 11%40% in poorly drained sites. Model simulations show that fire intervals <60 years lead to the local extinction of black spruce, and those >220 years lead to that of jack pine. The simulation results also suggest that jack pine could expand its populations under a fire cycle of 50 years or after short fire intervals during longer fire cycles. Thus, in the short term and medium term (i.e., ca. <100 years), the length of the interval between two consecutive fires is a better predictor of the abundance, extinction, or local expansion of black spruce and jack pine than the fire cycle.
Bidirectional introgression betweenPinus taedaandPinus echinata: evidence from morphological and molecular data
Authors: Chen Jiwang , Tauer C G , Bai Guihua , Huang Yinghua , Payton M E , Holley A G
Published: January 2005

The frequency of mature hybrids, including post-F1individuals, between loblolly (Pinus taeda L.) and shortleaf pine (Pinus echinata Mill.), detectable with a codominant nuclear marker, was studied in a sympatric population from central Arkansas. The direction of introgression was also examined. The marker revealed 10 putative hybrids from the 80 trees sampled. PCR-RFLP analysis of their rbcL gene showed two of the putative hybrids (HL) share loblolly pine chloroplast DNA, and eight (HS) share the shortleaf pine chloroplast DNA. The two putative HL hybrids were morphologically similar to loblolly pine, and the eight putative HS hybrids were morphologically similar to shortleaf pine. Utilizing microsatellite data, Nei's measure of genetic identity showed the putative HL hybrids to be similar to loblolly pine, and the putative HS hybrids as being similar to shortleaf pine. An inferred tree of the individuals, using simple sequence repeat data and the neighbor-joining method, also suggested that some of the putative hybrids were not F1individuals. Principle component analysis of the morphological characters groups the HL trees with loblolly pine and the HS trees with shortleaf pine. These results suggest bidirectional introgression occurred within the study population, and some of the putative hybrids were likely derived from early-generation backcross(es) with either shortleaf or loblolly pine.
Susceptibility of pine plantations to attack by the pine shoot beetle (Tomicus piniperda) in southern Ontario
Authors: Morgan Ryan E , Groot Peter de , Smith Sandy M
Published: January 2005

The pine shoot beetle, Tomicus piniperda (L.) (Coleoptera: Scolytidae), was first discovered in North America in 1992, and by the late 1990s it was associated with tree mortality and stand decline throughout southern Ontario. To assess whether this beetle was capable of killing vigorous trees (a primary pest) or would kill only trees already stressed (a secondary pest), we surveyed 43 sites of varying Scots pine (Pinus sylvestris L.), red pine (Pinus resinosa Ait.), and jack pine (Pinus banksiana Lamb.) composition. Specifically, our objective was to determine the relationship between tree and site characteristics and the number of stem and shoot attacks by T. piniperda in southern Ontario. An abundance of recently dead and low-vigour pine trees increased susceptibility of sites to stem and shoot attacks by T. piniperda. Significant negative linear relationships were detected between the number of beetle attacks and the mean height, age, diameter at breast height, basal area, canopy cover, duff depth, and radial growth increments. Pure red pine sites had significantly fewer attacks than sites of pure Scots pine and mixed jack pine, which was attributed to differences in tree vigour and forest management. Tomicus piniperda appears to be a secondary bark beetle in southern Ontario, successfully colonizing only recently dead pine trees or trees suffering from stress.
Ecological status of American chestnut (Castaneadentata) in its native range in Canada
Authors: Tindall Jeffrey R , Gerrath John A , Melzer Melody , McKendry Karen , Husband Brian C , Boland Greg J
Published: January 2005

American chestnut (Castanea dentata (Marsh.) Borkh.) was once a dominant tree in eastern deciduous forests of North America and is now endangered in Canada, primarily because of the introduction of a fungal pathogen (Cryphonectria parasitica (Murrill) Barr) causing chestnut blight. A recovery plan is being developed, and more accurate information on the status of this species in its native range in southern Ontario is needed to assist in the restoration and management of this species. We conducted a 2-year inventory of the distribution and size of trees throughout southern Ontario, and characterized the habitat and incidence of blight. In total, 682 trees were sampled, 601 of which were not planted. Individuals were statistically most likely to occur in deciduous forest habitats with high canopy cover (>50%), gentle slopes (0°10°), and acidic (pH 46), sandy (>75%) soils. Most trees were small (80% were <20 cm diameter at breast height (DBH)) and nonreproductive (86%). Blight cankers were visible on only 25% of trees. Of six habitat variables measured, canopy cover was positively related to tree size (height, DBH) and incidence of blight. Litter depth was also a good predictor of cankers and virulent cankers in particular, but not healing and (or) healed cankers. The presence of Acer and Quercus spp. in the canopy was associated with reduced incidence and number of cankers per tree but increased frequencies of healing and (or) healed cankers, while Carya was correlated with increased incidence and number of cankers per tree. The abundance of American chestnut and the number of blight-free trees in southern Ontario is higher than previously known. The importance of canopy density and associated species in the habitat for tree health will contribute to the development of further research programs and management strategies for the restoration of this endangered species.
TRANSPORT PROPERTIES OF A CHAIN WITH RANDOMLY ATTACHED DIMER IMPURITIES
Authors: HU DONG-SHENG , XIONG SHI-JIE , WU XING-LONG
Published: January 2005

Transport properties of a one-dimensional (1D) chain with randomly attached dimer impurities are investigated. Using the transfer-matrix technique, we present numerical results of the transmission coefficient as a function of the electron energy. It is found that an extended state exists in such a random 1D system and many resonant energies appear in periodic conditions. We present an analytic expression for the energy of the extended state which is determined by the potential of dimer-impurity and the hopping between the dots of the dimer.
TEMPERATURE-DEPENDENT THERMOELECTRIC POWER OF CuO, ZnO AND TiO2 SUBSTITUTED FOR PbO IN EUTECTIC LEAD VANADATE GLASS SYSTEM
Authors: RAMESH K. V. , SASTRY D. L. , PURUSHOTHAM Y.
Published: January 2005

Temperature-dependence of the thermoelectric power of the semi-conducting CuO , ZnO and TiO 2 substituted for PbO in eutectic lead vanadate glasses was presented in a range of compositions. The high-temperature thermoelectric power was satisfactorily explained by Heikes' relation and the data also showed evidence of small polaron formation in thesae glasses. Thermo EMF measurements indicate that all the glass samples including unsubstituted lead metavanadate are n-type at room temperature. As temperature is increased ZnO and TiO 2 substituted samples change from n-type to p-type. The CuO substituted system remains n-type like the unsubstituted system even at high temperatures. When Heike's formula is applied to all the systems at room temperature, the amount of disorder was found to be the same in all the systems. When Emin's formula is used for the estimation of WD, the activation energy due to disorder, in ZnO and TiO 2 substituted samples, unusually large values of WD (~ 0.6 eV) are obtained. The present results indicate that the Emin's formula cannot be directly used to estimate the disorder energy in ZnO and TiO 2 sustituted lead vanadates. The temperature dependent change of sign of the thermoelectric power S, in these systems may arise due to change in V 4+/ V 5+ ratio with the change of temperature or due to the onset of band type of conduction as in MnO or other extrinsic compensated semi-conductors.
ON THE INTERPRETATION OF THE NERNST EFFECT MEASUREMENTS IN THE CUPRATES
Authors: USSISHKIN IDDO , SONDHI S. L.
Published: January 2005

We consider the large Nernst signal discovered by Ong and collaborators in hole-doped cuprates, in particular in the pseudogap regime. Based on our previous quantitative calculations together with Huse [Phys. Rev. Lett.89, 287001 (2002)], we discuss the interpretation of the experimental observations as arising from superconducting fluctuations and its relation to the vortex scenario proposed by Ong. We also comment on the implications of the Nernst analysis for understanding the full range of pseudogap phenomena.
NONLINEAR FILTERING OF SMOOTH SIGNALS
Authors: KHASMINSKII R.
Published: January 2005

A nonlinear online Kalman type filter is proposed for the estimation of unknown function S(t) with the known smoothness β for the diffusion observed process with small, of the order ε2, diffusion coefficient. Assuming that the drift coefficient of the observed process depends on an unknown function S(t), we propose an approach to the analysis of this estimator based on the Lyapunov's functions method. The best possible rate of convergence of risks to 0, as ε → 0, is proven for β ≤ 2.
THE RESTRICTION OF THE FRACTIONAL ITÔ INTEGRAL TO ADAPTED INTEGRANDS IS INJECTIVE
Authors: BENDER CHRISTIAN
Published: January 2005

We prove that the Wick–Itô–Skorohod integral with respect to a fractional Brownian motion is injective when it is restricted to a class of adapted integrands that satisfy an appropriate integrability condition.
BOUNDARIES OF ATTRACTORS AS OMEGA LIMIT SETS
Authors: ROBINSON JAMES C. , TEARNE OLIVER M.
Published: January 2005

When a system of ordinary differential equations on ℜd have an attractor [Formula: see text] given as the omega-limit set of a compact set [Formula: see text], then provided that D contains [Formula: see text] necessarily [Formula: see text], i.e. the boundary of the attractor is the omega-limit set of the boundary of D. In general only a weaker result, [Formula: see text], can be shown to hold for random attractors arising from systems of stochastic ordinary differential equations, where now D is any compact set such that [Formula: see text] is contained in D with a positive probability. However, if in addition [Formula: see text] is empty with positive probability, then in fact [Formula: see text].
Open Source to the Core
Authors: Hubbard Jordan
Published: January 2005

The open source development model is not exactly new. Individual engineers have been using open source as a collaborative development methodology for decades. Now that it has come to the attention of upper and middle management, however, it’s finally being openly acknowledged as a commercial engineering force-multiplier and important option for avoiding significant software development costs.
From IR to Search, and Beyond
Authors: Rao Ramana
Published: January 2005

It’s been nearly 60 years since Vannevar Bush’s seminal article, ’As We May Think,’ portrayed the image of a scholar aided by a machine, “a device in which an individual stores all his books, records, and communications, and which is mechanized so that it may be consulted with exceeding speed and flexibility.”
A Conversation with Brewster Kahle
Authors: Feldman Stu
Published: January 2005

Stu Feldman, Queue board member and vice president of Internet technology for IBM, interviews the chief executive officer of the nonprofit Internet Archive.
From This Moment On
Authors: Kelly-Bootle Stan
Published: January 2005

Science fiction seems to have spawned two divergent subgenres. One, which is out of favor, paints a bright future for us, assuming an optimistic, Darwinian "perfectability." These scenarios project an ever-expanding (or rather, a never-imploding) cosmos with ample time for utopian evolutions.
From the Editors: Virtually Yours
Authors: Grossman Edward
Published: January 2005

It’s one of those names that’s so bad you just have to use it. It reminds me of the hair salons you find in small towns. And believe it or not, hairstyling is not unrelated to the topic of this month’s special report, virtual machines: they’re both subject to the whims of fashion.
Opinion: For Want of a Comma, the Meaning Was Lost
Authors: Raskin Jef
Published: January 2005

Odder things have happened in publishing, but not by much. The bestseller list on Amazon (as I write this) is topped by Lynne Truss’s book on... punctuation. It’s outselling Harry Potter. Starting from the title, ’Eats, Shoots and Leaves’ (Gotham Books, 2004), which changes meaning drastically when the comma is omitted, the book is an entertaining romp through the advantages of writing correctly and clearly with the proper use of punctuation.
Segmented channel routability via satisfiability
Authors: Hung William N. N. , Song Xiaoyu , Aboulhamid El Mostapha , Kennings Andrew , Coppola Alan
Published: January 2005

Segmented channel routing is fundamental to the routing of row-based FPGAs. In this paper, we study segmented channel routability via satisfiability. Our method encodes the horizontal and vertical constraints of the routing problem as Boolean conditions. The routability constraint is satisfiable if and only if the net connections in the segmented channel are routable. Empirical results show that the method is time-efficient and applicable to large problem instances.
Combining 4- and 3-direction subdivision
Authors: Peters Jörg , Shiue Le-Jeng
Published: January 2005

4-3 direction subdivision combines quad and triangle meshes. On quad submeshes it applies a 4-direction alternative to Catmull-Clark subdivision and on triangle submeshes a modification of Loop's scheme. Remarkably, 4-3 surfaces can be proven to be C1 and have bounded curvature everywhere. In regular mesh regions, they are C2 and correspond to two closely-related box-splines of degree four. The box-spline in quad regions has a smaller stencil than Catmull-Clark and defines the unique scheme with a 3 × 3 stencil that can model constant features without ripples both aligned with the quad grid and diagonal to it. From a theoretical point of view, 4-3 subdivision near extraordinary points is remarkable in that the eigenstructure of the local subdivision matrix is easy to determine and a complete analysis is possible. Without tweaking the rules artificially to force a specific spectrum, the leading eigenvalues ordered by modulus of all local subdivision matrices are 1, 1/2, 1/2, 1/4 where the multiplicity of the eigenvalue 1/4 depends on the valence of the extraordinary point and the number of quads surrounding it. This implies equal refinement of the mesh, regardless of the number of neighbors of a mesh node.
A signal-processing framework for reflection
Authors: Ramamoorthi Ravi , Hanrahan Pat
Published: January 2005

We present a signal-processing framework for analyzing the reflected light field from a homogeneous convex curved surface under distant illumination. This analysis is of theoretical interest in both graphics and vision and is also of practical importance in many computer graphics problems---for instance, in determining lighting distributions and bidirectional reflectance distribution functions (BRDFs), in rendering with environment maps, and in image-based rendering. It is well known that under our assumptions, the reflection operator behaves qualitatively like a convolution. In this paper, we formalize these notions, showing that the reflected light field can be thought of in a precise quantitative way as obtained by convolving the lighting and BRDF, i.e. by filtering the incident illumination using the BRDF. Mathematically, we are able to express the frequency-space coefficients of the reflected light field as a product of the spherical harmonic coefficients of the illumination and the BRDF. These results are of practical importance in determining the well-posedness and conditioning of problems in  inverse rendering---estimation of BRDF and lighting parameters from real photographs. Furthermore, we are able to derive analytic formulae for the spherical harmonic coefficients of many common BRDF and lighting models. From this formal analysis, we are able to determine precise conditions under which estimation of BRDFs and lighting distributions are well posed and well-conditioned. Our mathematical analysis also has implications for forward rendering---especially the efficient rendering of objects under complex lighting conditions specified by environment maps. The results, especially the analytic formulae derived for Lambertian surfaces, are also relevant in computer vision in the areas of recognition, photometric stereo and structure from motion.
On the support of recursive subdivision
Authors: Ivrissimtzis Ioannis P. , Sabin Malcolm A. , Dodgson Neil A.
Published: January 2005

We study the support of subdivision schemes: that is, the region of the subdivision surface that is affected by the displacement of a single control point. Our main results cover the regular case, where the mesh induces a regular Euclidean tesselation of the local parameter space. If n is the ratio of similarity between the tesselations at steps k and k − 1 of the refinement, we show that n determines the extent of this region and largely determines whether its boundary is polygonal or fractal. In particular if n = 2 (or n2 = 2 because we can always take double steps) the support is a convex polygon whose vertices can easily be determined. In other cases, whether the boundary of the support is fractal or not depends on whether there are sufficient points with non-zero coefficients in the edges of the convex hull of the mask. If there are enough points on every such edge, the support is again a convex polygon. If some edges have enough points and others do not, the boundary can consist of a fractal assembly of an unbounded number of line segments.
Review of "Handbook of Graph Theory edited by Gross and Yellen." CRC, 2004.
Authors: Gasarch William
Published: January 2005

One uses a handbook by looking up things that you always wanted to know or that come up. Hence, I decided to review this handbook by asking a random collection of theorists (the editors of SIGACT NEWS and theorists in the Maryland-Wash DC area) to email me questions they are either curious about or think ought to be in a handbook. I comment on how well the book does on answering each one, and then summarize how well the book did overall. For each question asked I looked rather carefully in the table of contents and the index; hence, if I say 'the book did not have anything on topic X' and in reality it does, then the books organization is at fault.
Guest column
Authors: Guruswami Venkatesan
Published: January 2005

The central algorithmic problem in coding theory is the construction of explicit error-correcting codes with good parameters together with fast algorithms for encoding a message and decoding a noisy received word into the correct message. Over the last decade, significant new developments have taken place on this problem using graph-based/combinatorial constructions that exploit the power of expander graphs. The role of expander graphs in theoretical computer science is by now certainly well-appreciated. Here, we will survey some of the highlights of the use of expanders in constructions of error-correcting codes.
ACM SIGACT news distributed computing column 15
Authors: Rajsbaum Sergio
Published: January 2005

The Distributed Computing Column covers the theory of systems that are composed of a number of interacting computing elements. These include problems of communication and networking, databases, distributed shared memory, multiprocessor architectures, operating systems, verification, Internet, and the Web.

This issue contains two items:

• An eulogy in memory of Shimon Even, who passed away on May 1st, 2004. He was a highly influential educator, and played a major role in establishing computer science education in Israel. He did pioneering work in various areas, including parallel and distributed computing. As Oded Goldreich says in his PODC 2004 proceedings eulogy, Shimon Even was a great scientist and a remarkable person. His attitudes toward research have influenced anybody who was fortunate to have an interaction with him, he always followed his own judgment and understanding, rather than the common trend or fashion. He sought simple solutions that uncover the essence of the problem. He spent much time seeking the best way to present his own work as well as the work of others in lectures and writing. This quote comes to mind, about having found a good problem to work on.

Not that I quite know indeed what situations the seeking fabulist does "find"; he seeks them enough assuredly, but he discoveries are, like those of the navigator, the chemist, the biologist, scarce more than alert recognitions. He comes upon the interesting thing as Columbus came upon the isle of San Salvador, because he had moved in the right direction for it---also because he knew, with the encounter, what "making land" then and there represented.

Henry James

• The 2004 Gödel Prize is great news for the distributed computing community: it is shared between two journal papers that discovered a fundamental relation between distributed computing and topology, by Maurice Herlihy and Nir Shavit, and Michael Saks and Fotios Zaharoglou. To celebrate this, I am happy to present personal perspectives by the authors of these papers, and by Elizabeth Borowsky and Eli Gafni, that coauthored a third paper with the discovery, but only in a conference and hence not eligible for the prize. I include perspectives also by other people that produced seminal work on the same subject: Soma Chaudhuri and Shlomo Moran.

The DISC conference is collocated this year with GETCO, a workshop on topological methods in concurrency and distributed computing. They will dedicate a joint session to celebrate the prize.

Many thanks to the contributors of this issue.
Chicago blues
Authors: Ross Rocky
Published: January 2005

I was at STOC this year. At least part of the time. Chicago is a remarkable city, especially so when the Blues Festival is underway. What a contrast! The Chicago Hilton on South Michigan Avenue was the venue of STOC; Grant Park across from the hotel on the shores of Lake Michigan was the site of the Blues Festival---a seething melting pot of languages, skin colors, smells, street food, and the soul-tugging strains of the blues wafting in from all angles. What to do? Listen to the blues being chanted in the general monotone voice of conference presentations ("well, we were able to prove this much, but, by golly, the next step seems elusive...") or the blues being sung on park greens in deep, throaty tones to the accompaniment of a wailing saxophone ("My wife left me for a rhinestone cowboy and the dog just overdosed on asparagus...")? The answer of course, was: A lot of both. Somehow, as you might well imagine, the contrast between STOC and the Blues Festival was almost enough to warp a person's mind (were it not already warped). Ditto for the contrast between the Chicago skyscrapers and the cloud piercing peaks of the Rocky Mountains of Bozeman.
What *is* information security?
Authors: Spafford Gene
Published: January 2005

Recent events have increasingly focused public attention on issues of information privacy, computer and network security, cybercrime and cyber terrorism. Yet despite all of this attention, there is some confusion about what is actually encompassed by those terms. There are some obvious components, such as cryptography and access control. However, the list of undisputed topics is not long or well-developed, and many questions arise as to whether a typical computer science department can offer all of the topics involved. That there are only a few universities that teach a comprehensive curriculum in these topics serves to illustrate the imprecise nature of the field. Many professionals have taken to describing it as "information security" or "information assurance" to distinguish that the focus is not on computers and networks, but on the information they hold and process.This talk will present a more comprehensive view of the area than simply within the confines of CS/CE. The speaker has been teaching information security for nearly 20 years and has developed a view that spans many traditional disciplines. The talk will present some of the reasons for that breadth of view, illustrated with examples taken from the recent CRA Grand Challenges Conference on Information Security. One conclusion from this talk is that getting good information security education widely implemented may not be simple, given current constraints and traditions within academia.
Debugging
Authors: Chmiel Ryan , Loui Michael C.
Published: January 2005

We conducted a study to demonstrate that formal training in debugging helps students develop skills in diagnosing and removing defects from computer programs. To accomplish this goal in an assembly language course, we designed multiple activities to enhance students' debugging skills. These activities included debugging exercises, debugging logs, development logs and reflective memos, and collaborative assignments. In a previous paper, we reported positive qualitative results. Students agreed that formal debugging training enhanced their debugging skills. In this paper, we present positive quantitative results that support our previous qualitative results. Students who completed the optional debugging exercises spent significantly less time on debugging their programs than those who did not. Furthermore, we develop a model of debugging abilities and habits based on students' comments in their debugging logs, development logs, reflective memos, and evaluation surveys. Students and educators could use the model to diagnose students' current debugging skills and take actions to enhance their skills.
Using software testing to move students from trial-and-error to reflection-in-action
Authors: Edwards Stephen H.
Published: January 2005

Introductory computer science students rely on a
trial and error
approach to fixing errors and debugging for too long. Moving to a
reflection in action
strategy can help students become more successful. Traditional programming assignments are usually assessed in a way that ignores the skills needed for reflection in action, but software testing promotes the hypothesis-forming and experimental validation that are central to this mode of learning. By changing the way assignments are assessed--where students are responsible for demonstrating correctness through testing, and then assessed on how well they achieve this goal--it is possible to reinforce desired skills. Automated feedback can also play a valuable role in encouraging students while also showing them where they can improve.
Case studies for teaching usability engineering
Authors: Rosson Mary Beth , Carroll John M. , Rodi Con M.
Published: January 2005

A challenge in teaching usability engineering is providing appropriate hands-on project experience. Students need projects that are realistic enough to address meaningful issues, but manageable within one semester. We describe our use of online case studies to motivate and model course projects in usability engineering. The cases illustrate scenario-based usability methods, and are accessed via a custom browser. We summarize the content and organization of the case studies, several case-based learning activities, and students' reactions to the activities. We conclude with a discussion of future directions for case studies in HCI education.
Handwritten slides on a tabletPC in a discrete mathematics course
Authors: Golub Evan
Published: January 2005

There are a wide variety of ways to present information at the front of a classroom. These include chalk on a blackboard, markers on a whiteboard, pens on transparencies, and computer projection systems. While computer-based presentation systems provide many opportunities both in and out of the classroom, there may also be many limitations. In-class spontaneity and dynamic exposition might be restricted. Class preparation time might increase dramatically when compared to the amount required to prepare handwritten materials. Certain presentation techniques may no longer be available. This paper will introduce a computer-based presentation system modeled on handwritten transparencies. It will then discuss how it addresses the above issues as well as how it can be used in and out of the classroom. These will be explored in the context of its use while teaching an undergraduate discrete mathematics course.
Evaluating the effectiveness of a new instructional approach
Authors: Moskal Barbara , Lurie Deborah , Cooper Stephen
Published: January 2005

This paper describes the evaluation of an NSF-sponsored educational research project. The primary focus of this project was to develop and evaluate a course curriculum designed to improve retention and performance for "at risk" introductory computer science majors. The results of this research suggest that the newly developed course and curriculum materials did improve students' performance and retention in computer science and their attitudes towards computer science.
The dream of a common language
Authors: Roberts Eric
Published: January 2005

In recent years, the languages, paradigms, and tools used to teach computer science have become increasingly complex. This added complexity puts pressure on designers of introductory courses, who must cover more material in an already overcrowded syllabus. The problem of complexity is exacerbated by the fact that languages and tools change quickly, which leads to profound instability in the manner in which computer science is taught. The situation has reached a point where it is difficult for individual computer science teachers to keep up. This paper examines the factors that promote complexity and instability in computer science. It then goes on to argue that we, as educators, must take responsibility for breaking this cycle of rapid obsolescence by developing a stable and effective collection of Java-based teaching resources that will meet the needs of the computer science education community. Such an initiative is already in progress under the direction of a special task force appointed by the ACM Education Board. The charter and current plans for that task force are being presented in a special session at this symposium.
Redesigning introductory computer programming with HTML, JavaScript, and Java
Authors: Mahmoud Qusay H. , Dobosiewicz Wlodek , Swayne David
Published: January 2005

In this paper we describe our experience in the design and teaching of a new evolutionary introductory programming course in a new Distributed Computing and Communications Systems Technology program at the University of Guelph-Humber. This course is evolutionary and innovative because it integrates the use of HTML, JavaScript, and Java in a one-semester introductory computer programming course. This is a marked departure from the use of a single conventional, general purpose, programming language such as Java or C++. The course is designed with two goals in mind: to improve the students experience in their first computer programming; and to achieve retention in the new program.
The Quiver system
Authors: Ellsworth Christopher C. , Fenwick James B. , Kurtz Barry L.
Published: January 2005

The Quiver (QUIz VERification) System is an Internet server for building, maintaining, and administering programming quizzes. It is similar to the online judges used for programming contests but differs in that it targets the classroom use of programming quizzes as a teaching aid and evaluation tool. It can provide very detailed feedback regarding quiz behavior so that the student can debug her program. This system is developed as part of the grant "Intra-Curriculum Software Engineering Education" funded by the National Science Foundation (DUE 0127439).
Enhancing lisp instruction with RCXLisp and robotics
Authors: Klassner Frank
Published: January 2005

This paper presents the RCXLisp library, an extension to Common Lisp that allows students to investigate a broad range of artificial intelligence and computer science topics using the LEGO MindStorms® platform. The library has two features that distinguish it from other third-party packages and languages designed by academics and hobbyists for programming the MindStorms platform. The first is that it supports both remote control and on-board programming of MindStorms robots. The second is that it supports targeted communication between multiple LEGO robots and command-center desktops. The package is also the only one to be integrated into most popular Common Lisp programming environments. This paper also summarizes student experiences with the package over the years 2000-2003 in an Artificial Intelligence course.
Implementation challenges for a K-12 computer science curriculum
Authors: Tucker Allen , McCowan Dennis , Deek Fadi , Stephenson Chris , Jones Jill , Verno Anita
Published: January 2005

This special session will report on the work of the ACM K-12 Computer Science Curriculum Committee, which recently completed the design of a K-12 model curriculum [1]. This session is a follow-up to our special session at SIGCSE 2003, which presented the first draft of that curriculum design. This session differs from that one by emphasizing the next steps that must be taken to implement the recommendations in the model.
Scheme-based web programming as a basis for a CS0 curriculum
Authors: Hickey Timothy J.
Published: January 2005

The thesis of this paper is that Scheme-based web programming is a worthy organizing topic for CS0 computer literacy courses. We describe an approach to introducing non-science majors to Computer Science by teaching them to write webpages using HTML and CSS and to also write applets and servlets using Scheme. The programming component of our approach is completed in about nine weeks of a thirteen week course, leaving time for a treatment of more traditional CS0 topics such as intellectual property, privacy, artificial intelligence, the limits of computability, PC architecture, Operating Systems, CMOS and logic circuits. We argue that the use of a high level scripting language (like Scheme) is essential to the success of this approach. We also argue that wide scale success in teaching web programming to non-majors could enhance the students productivity when they enter the job market, and hence this approach deserves further study.
Events not equal to GUIs
Authors: Hansen Stuart , Fossum Timothy
Published: January 2005

The event driven paradigm is ubiquitous in modern software. Many texts introduce events when discussing graphical user interfaces, but the event paradigm extends well beyond that domain. Events also play important roles in operating systems, component based systems, reactive systems, middleware, web services and other fields. Computer science educators have an obligation to see that our students thoroughly understand the event paradigm and have some grounding in tools to develop event driven systems. This paper describes an upper division, computer science elective course in event driven programming. The course gives a comprehensive treatment of event driven systems. It appropriately captures the importance of the event paradigm and serves to integrate concepts from several different computing fields, including Programming Languages, Operating Systems, and Software Engineering. It also introduces students to advanced tools and packages designed for developing event driven systems. The course has been taught four times at our institution, having repeatedly received high marks from the students for both its conceptual and technical content.
Tele-lab IT security
Authors: Hu Ji , Meinel Christoph , Schmitt Michael
Published: January 2005

IT security education is an important activity in computer science education. The broad range of existing security threats makes it necessary to teach students the principles of IT security as well as to let them gain hands-on experience. In order to enable students to practice IT security anytime anywhere, a novel tutoring system is being developed at the University of Trier, Germany, which allows them to get familiar with security technologies and tools via the Internet. Based on virtual machine technology, users are able to perform exercises on a Linux system instead of in a restricted simulation environment. This paper describes the user interface of the Tele-Lab IT Security, its system architecture and its functional components.
We claim this class for computer science
Authors: Decker Adrienne , Ventura Phil
Published: January 2005

We have recently launched a reorganized discrete structures course being taught in the computer science department for computer science majors. The main idea of the reorganization is to make the course relevant and productive for the computer science students. During the Spring of 2003, students who were taking both discrete structures and CS2 commented that taking both courses at the same time was helpful. An empirical investigation was conducted to see if there was a benefit to students taking both courses concurrently. The results show that there was a benefit to students taking both courses. The students who were taking both courses were performing better in discrete structures than those students who were not.
Electronic commerce software laboratory
Authors: Weaver Alfred C.
Published: January 2005

With NSF support we developed a hands-on laboratory to augment our CS453 Electronic Commerce Technologies course. We conducted weekly lab sessions that covered HTML, CSS, JavaScript, Perl, CGI, SQL, ASP, and Flash programming. Each topic was covered over a period of one to three weeks and each topic was supported by 10 to 26 individual programming exercises. Four teaching assistants provided real-time support during the laboratory period. Answers to all exercises were accessible on-line so that no student would be needlessly delayed by any particular problem. In this paper we discuss the laboratory's design goals, topical content, and the students' performance, reactions, and suggestions for improvement.
Wire Delay is Not a Problem for SMT (In the Near Future)
Authors: Vijaykumar T. N. , Chishti Zeshan
Published: January 2005

Previous papers have shown that the slow scaling of wiredelays compared to logic delays will prevent superscalar performancefrom scaling with technology.In this paper we showthat the optimal pipeline for superscalar becomes shallowerwith technology, when wire delays are considered, tighteningprevious results that deeper pipelines perform only as well asshallower pipelines.The key reason for the lack of performancescaling is that superscalar does not have sufficient parallelismto hide the relatively-increased wire delays.However,Simultaneous Multithreading (SMT) provides the much-neededparallelism.We show that an SMT running a multiprogrammedworkload with just 4-way issue not only retains theoptimal pipeline depth over technology generations, enablingat least 43% increase in clock speed every generation, but alsoachieves the remainder of the expected speedup of two pergeneration through IPC.As wire delays become more dominantin future technologies, the number of programs needs tobe scaled modestly to maintain the scaling trends, at least tillthe near-future 50nm technology.While this result ignoresbandwidth constraints, using SMT to tolerate latency due towire delays is not that simple because SMT causes bandwidthproblems.Most of the stages of a modern out-of-order-issuepipeline employ RAM and CAM structures.Wire delays in conventional,latency-optimized RAM/CAM structures preventthem from being pipelined in a scaled manner.We show thatthis limitation prevents scaling of SMT throughput.We use bitlinescaling to allow RAM/CAM bandwidth to scale with technology.Bitline scaling enables SMT throughput to scale at therate of two per technology generation in the near future.
Single-ISA Heterogeneous Multi-Core Architectures for Multithreaded Workload Performance
Authors: Kumar Rakesh , Tullsen Dean M. , Ranganathan Parthasarathy , Jouppi Norman P. , Farkas Keith I.
Published: January 2005

A single-ISA heterogeneous multi-core architecture is achip multiprocessor composed of cores of varying size, performance,and complexity. This paper demonstrates that thisarchitecture can provide significantly higher performance inthe same area than a conventional chip multiprocessor. It doesso by matching the various jobs of a diverse workload to thevarious cores. This type of architecture covers a spectrum ofworkloads particularly well, providing high single-thread performancewhen thread parallelism is low, and high throughputwhen thread parallelism is high.This paper examines two such architectures in detail,demonstrating dynamic core assignment policies that providesignificant performance gains over naive assignment, andeven outperform the best static assignment. It examines policiesfor heterogeneous architectures both with and withoutmultithreading cores. One heterogeneous architecture we examineoutperforms the comparable-area homogeneous architectureby up to 63%, and our best core assignment strategyachieves up to 31% speedup over a naive policy.
Power Awareness through Selective Dynamically Optimized Traces
Authors: Rosner Roni , Almog Yoav , Moffie Micha , Schwartz Naftali , Mendelson Avi
Published: January 2005

We present the PARROT concept that seeks to achievehigher performance with reduced energy consumptionthrough gradual optimization of frequently executed codetraces. The PARROT microarchitectural framework integratestrace caching, dynamic optimizations and pipelinedecoupling. We employ a selective approach for applyingcomplex mechanisms only upon the most frequently usedtraces to maximize the performance gain at any givenpower constraint, thus attaining finer control of tradeoffsbetween performance and power awareness.We show that the PARROT based microarchitecture canimprove the performance of aggressively designed processorsby providing the means to improve the utilizationof their more elaborate resources. At the same time, rigorousselection of traces prior to storage and optimizationprovides the key to attenuating increases in thepower budget.For resource-constrained designs, PARROT based architecturesdeliver better performance (up to an average16% increase in IPC) at a comparable energy level,whereas the conventional path to a similar performanceimprovement consumes an average 70% more energy.Meanwhile, for those designs which can tolerate a higherpower budget, PARROT gracefully scales up to use additionalexecution resources in a uniformly efficient manner.In particular, a PARROT-style doubly-wide machinedelivers an average 45% IPC improvement while actuallyimproving the cubic-MIPS-per-WATT power awarenessmetric by over 50%.
X-RAY
Authors: Bairavasundaram Lakshmi N. , Sivathanu Muthian , Arpaci-Dusseau Andrea C. , Arpaci-Dusseau Remzi H.
Published: January 2005

RAID storage arrays often possess gigabytes of RAM forcaching disk blocks. Currently, most RAID systems use LRUor LRU-like policies to manage these caches. Since these arraycaches do not recognize the presence of file system buffer caches,they redundantly retain many of the same blocks as those cachedby the file system, thereby wasting precious cache space. In thispaper, we introduce X-RAY, an exclusive RAID array cachingmechanism. X-RAY achieves a high degree of (but not perfect) exclusivitythrough gray-box methods: by observing which files havebeen accessed through updates to file system meta-data, X-RAYconstructs an approximate image of the contents of the file systemcache and uses that information to determine the exclusive set ofblocks that should be cached by the array. We use microbenchmarksto demonstrate that X-RAY's prediction of the file systembuffer cache contents is highly accurate, and trace-based simulationto show that X-RAY considerably outperforms LRU andperforms as well as other more invasive approaches. The mainstrength of the X-RAY approach is that it is easy to deploy - allperformance gains are achieved without changes to the SCSI protocolor the file system above.
Prophet/Critic Hybrid Branch Prediction
Authors: Falcon Ayose , Stark Jared , Ramirez Alex , Lai Konrad , Valero Mateo
Published: January 2005

This paper introduces the prophet/critic hybrid conditionalbranch predictor, which has two component predictorsthat play the role of either prophet or critic.Theprophet is a conventional predictor that uses branch historyto predict the direction of the current branch.Further accessesof the prophet yield predictions for the branches followingthe current one.Predictions for the current branchand the ones that follow are collectively known as thebranch's future.They are actually a prophecy, or predictedbranch future.The critic uses both the branch's history andfuture to give a critique of the prophet's prediction fo thecurrent branch.The critique, either agree or disagree, isused to generate the final prediction for the branch.Our results show an 8K + 8K byte prophet/critic hybridhas 39% fewer mispredicts than a 16K byte 2Bc-gskewpredictor-a predictor similar to that of the proposed Compaq*Alpha* EV8 processor-across a wide range of applications.The distance between pipeline flushes due to mispredictsincreases from one flush per 418 micro-operations(uops) to one per 680 uops.For gcc, the percentage of mispredictedbranches drops from 3.11% to 1.23%.On a machinebased on the Intel® Pentium® 4 processor, this improvesuPC (Uops Per Cycle) by 7.8% (18% for gcc) andreduces the number of uops fetched (along both correct andincorrect paths) by 8.6%.