Integrated videos and maps for driving directions While onboard navigation systems are gaining in importance, maps are still the medium of choice for laying out a route to a destination and for way finding. However, even with a map, one is almost always more comfortable navigating a route the second time due to the visual memory of the route. To make the first time navigating a route feel more familiar, we present a system that integrates a map with a video automatically constructed from panoramic imagery captured at close intervals along the route. The routing information is used to create a variable speed video depicting the route. During playback of the video, the frame and field of view are dynamically modulated to highlight salient features along the route and connect them back to the map. A user interface is demonstrated to allow exploration of the combined map, video, and textual driving directions. We discuss the construction of the hybrid map and video interface. Finally, we report the results of a study that provides evidence of the effectiveness of such a system for route following. Finding one's way to a destination has for centuries depended on the use of maps. Today, we are offered interactive maps that can draw a route, generate textual descriptions of routes, and provide interactive panning and zooming. Yet, even with these resources, the first time we navigate our way to a new destination we are uncertain of our way, having no visual Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. memory to rely on. Once we have driven a route, the next time is invariably much easier as our visual memory both gives us confidence and provides visual cues about what is approaching and where we should turn.. Companies such as Google and Microsoft have now driven a large number of the cities streets capturing 360 degree panoramas every few meters. These are delivered in, for example, Google's Streetview application. This data now provides new opportunities for almost any location to add visual previews to maps and textual descriptions. We show how the collected images can also provide a proxy visual experience of driving the route for the first time in the form of a video. Coupling this experience with more traditional maps and textual instructions leads to a new interface which we demonstrate.. This interface integrates an online map with an automatically generated summary video of the driving route. The goal of the interface is to enable the user to better understand his/her driving route, by interacting with the map and video. The integrated interface and the summary video are outputs of the system.. Although providing a literal video of the route would be trivial, few people would want to sit through a 20 minute video of a 20 minute drive. Simply speeding up the video 20 fold to create a one minute video would result in a useless blur. We demonstrate a method to automatically vary the speed of travel along the route to highlight turns and landmarks.. A video that always looks straight along the travel direction would miss landmarks as they pass by and would be jarring at turns. We demonstrate automatically generated videos that vary the field of view, aspect ratio, and view direction to provide a useful proxy for driving the route (see Figure 1) . Finally, we integrate the video within an interactive mapping application that includes graphical and textual routes interspersed with video cliplets and the route video itself. We also report the results of a study of the effectiveness of our system.. We realize that in vehicle GPS and navigation systems may somewhat obviate the need for maps and the technology we introduce here. However, it will be some time before all cars have GPS systems. Future navigation systems might also incorporate similar rehearsal videos that depict approaching important landmarks and turns.. Our specific contributions thus include:. • Generation of a route video from a sequence of panoramas • Automatic speed control based on the route parameters • Automated orientation of the video to anticipate the route • Visualization of landmarks and key images at turns by varying the field-of-view • Integration of video into a mapping application • A user interface providing video cliplets within the textual descriptions and along a route A final contribution is the report of a user study that lends credence to the usefulness of a video preview. After a brief discussion of previous work, we describe and demonstrate each of the above aspects of our work. The study took an average of 45 minutes per user. We performed a two-way repeated measures analysis of variance (RM-ANOVA) on Success Rate and Looks. We found a significant effect for technique on Success Rate (F(1,36) = 4.113165; p = 0.002). The results show that on average users were more successful in navigating the driving turns after using the Videomap interface, as compared to using the Photomap interface. Figure 10 shows a plot of the mean success rate for both techniques. The difference in mean success rate was not statistically significant across the two datasets ((F(1,36) = 4.113165; p=0.99). This means that the differences between route A and B did not affect the mean success rate.. We also found a significant effect for technique on the number of Looks (F(1, 24) = 4.25967; p = 0.00177). The results indicate that on average Videomap users tended to rely less on the printed driving directions during the driving simulation. Figure 11 plots the number of Looks per decision point.. After performing each test, participants were asked to answer a questionnaire. When asked which technique he/she preferred, 17 out of 20 participants preferred the Videomap over the Photomap. Participants were also asked the following two questions for each technique: 1) When driving the video simulation, I needed the printed map and directions to navigate the turns. 2) When driving the video simulation, I needed more time to decide each turn. The questions were answered using a Likert scale (1 = strongly disagree, 5 = strongly agree). In both techniques, printed maps and driving directions were needed. However, when asked about needing more time, Photomap users on average agreed while Videomap users on average neither agreed or disagreed (F(1,36) = 4.113; p = 0.026). Figure 12 visualizes the mean and 95% confidence levels of the participants answers.. The responses to the questionnaire resonated well with their performance using both two techniques. The majority of the participants preferred the Videomap over the Photomap. The main reason is that the Videomap provides a visual context that is absent in a single image. This idea is exemplified well in several user comments. One participant noted, " [The] photos are too close to the intersections, forcing me to turn late. Videomap seemed easier, and I have years and years of maps experience." When looking at the thumbnails in the Photomap, another user said, "Which way am I coming from?" However, when using the Videomap, the same user said, "That's cool, it [the video] leads up to the waypoint." This comment shows that the Videomap provides a context to the turns, which is lacking in the Photomap.. While the study indicates quantitatively and qualitatively that the Videomap increases driver performance over the Photomap, the interface itself could also be improved. One concern that surfaced was that the Videomap had too many dynamic elements. Since the video and the map can both move, the users attention can be split between them. Intuitively, visual memory of a route aids in wayfinding a second time a route is navigated. This intuition was confirmed in To See But Not to See: A Case Study of Visual Agnosia [4] , where Humphreys and Riddoch discuss a patient who, because of an inability to form visual memories, has great difficulty finding his way along routes he commonly takes, even though he can draw a fairly accurate map of the route.. There are certainly differences across individuals with respect to how one performs wayfinding tasks. Jones and Healy [6] show that women orient themselves more by remembering landmarks while men use more abstract features such as maps. Combining both elements should optimize the recognition for both.. There is an extensive literature on wayfinding in the psychology literature related to maps, signage, etc. There have also been a number of studies on wayfinding in virtual worlds with and without using virtual reality (heads up) hardware or using driving simulators [1, 10] . If any conclusion can be drawn from such work, it is that different individuals use different strategies for wayfinding. Some are very visually oriented (remembering the way a route looks), while others are more spatially oriented (mentally building and remembering the 2D structure of the route). Adding a video preview to a map should help both categories of people since the spatial information is amended by visual aids.. A seminal work in creating flexible video views of routes was presented almost 30 years ago in MovieMaps [9] . We have not found subsequent work related directly to video previews of driving routes, most likely since this type of data has not been widely available until recently.. There has been significant work studying the relationship between mapped representations of routes vs textual representations [11, 3] which have generally found these types of descriptions to be complementary. Lee, Tappe, and Klippel [8] discuss the use of icons to represent landmarks within maps to help in route following.. We automatically adapt the video's speed to the salience of the local portion of the route. This was inspired by Linedrive, by Agrawala and Stolte [2] which renders geographic route maps in a schematic style to provide both detail near the start and end point of a route while maintaining a consistent layout of the complete route. The system uses an optimization function to select and score the elements of a given route. The recent MOVE system [7] uses a similar approach for invehicle navigation systems and demonstrates that with such an approach users can more quickly comprehend the local region. We use a similar mechanism to assign more time and space in the video for important visual features along the route.

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On the Ideals of Secant Varieties of Segre Varieties Abstract. We establish basic techniques for studying the ideals of secant varieties of Segre varieties. We solve a conjecture of Garcia, Stillman and Sturmfels on the generators of the ideal of the first secant variety in the case of three factors and solve the conjecture set-theoretically for an arbitrary number of factors. We determine the low degree components of the ideals of secant varieties of small dimension in a few cases. Let X n ⊂ PV be a projective variety. Define σ r (X), the variety of secant P r−1 's to X by σ r (X) = ∪ x 1 ,...,xr∈X P x 1 ,...,xr. where P x 1 ,...,xr ⊂ PV denotes the linear space spanned by x 1 , ..., x r (usually a P r−1 ).. Given X ⊂ PV and p ∈ PV define the essential X-rank of p (or essential rank of p if X is understood) to be the smallest r such that p ∈ σ r (X). (The essential rank is often called the border rank in the computational complexity literature.) Similarly define the rank of p to be the smallest r such that there exist r points on X, x 1 , ..., x r such that p ∈ P x 1 ,...,xr . The essential rank can be smaller than the rank, this phenomenon occurs already for X = v 3 (P 1 ), the cubic curve, where the essential rank of any point is at most two, but the rank of points on a tangent line to X (but not on X) is three.. Given vector spaces A 1 , ..., A k , one can form the Segre product X = Seg(PA 1 × · · · × PA k ) ⊂ P(A 1 ⊗ · · · ⊗ A k ). When k = 2, the Segre product is just the projectivization of the space of rank one elements (matrices) in A 1 ⊗ A 2 . In this paper we study the ideals of the varieties σ p (X). The case k = 3 is important in the study of computational complexity as explained below. Many cases are important in the study of Bayesian networks, as explained in [6] . After presenting some background information in §2, we establish basic techniques for studying the problem for an arbitrary rational homogeneous variety X in §3. In §4 we specialize to Segre products and take advantage of Schur duality. We determine I 3 (σ 2 (X)) for any Segre product in Theorem 4.7. We prove that I 3 (σ 2 (X)) cuts out σ 2 (X) set-theoretically in all cases and ideal theoretically when k = 3, partially resolving Conjecture 21 of [6] , see Theorem 5.1.. We present a deterministic algorithm to find generators of the ideals of secant varieties of Segre varieties in §4. We carry this algorithm out in low degrees in §6. In particular, we show there are no equations in the ideal of σ 6 (P 3 × P 3 × P 3 ) in degree less than nine. We plan to study higher degrees in a future paper.. One motivation for this paper is the following question in computational complexity: Let A = (C n ⊗ C m ) * , B = (C m ⊗ C p ) * , C = C n ⊗ C p . The matrix multiplication operator M nmp is an element of A ⊗ B ⊗ C. In standard coordinates M nmp is the sum of nmp monomials. However, already if one takes m = n = p = 2, it is known that σ 7 (P 3 × P 3 × P 3 ) = P 15 so the essential rank of M 222 is at most seven. Strassen showed [13] that in fact the rank is at most seven by exhibiting an explicit expression of M 222 as the sum of seven monomials, and moreover, he proved that the essential rank is at least six by a specialization argument. The rank of M 222 was then shown to be seven in [15] .. To determine the essential rank of a point p ∈ PV it is sufficient to find equation cutting out the varieties σ k (X) set theoretically and then to evaluate the polynomials at p. Thus once one finds equations of σ 6 (Seg(P 3 × P 3 × P 3 )) one can determine the essential rank of M 222 .. T [ x 1 +...+ xr] σ r (X) =T x 1 X + · · · +T xr X where x ∈ V denotes a point in the linex ⊂ V corresponding to the point x ∈ PV andT p Y ⊂ V denotes the affine tangent space to Y at p, the cone over the embedded tangent projective spacẽ T p Y ⊂ PV . If X n is smooth then the dimension of σ 2 (X) can be determined by taking three derivatives at a general point x ∈ X, see [7] . In particular, if the third fundamental form of X at x, III X,x , is non-zero, then σ 2 (X) is of the expected dimension 2n + 1.. The third fundamental form calculation immediately implies that all homogeneously embedded rational homogeneous varieties have σ 2 (X) of dimension 2dim X + 1 except for the following varieties (embeddings are the minimal homogeneous ones unless otherwise specified and if varieties occur more than one way we only list them once): G(2, n) = A n−1 /P 2 the Grassmanian of 2-planes through the origin in C n , Q 2n−1 = D n /P 1 , Q 2n−2 = B n /P 1 , the quadric hypersurfaces, G Q (2, 2n) = D n /P 2 , G Q (2, 2n + 1) = B n /P 2 , the Grassmanians of 2-planes throught the origin isotropic for a quadratic form, v 2 (P n ) the quadratically embedded Veronese, G ω (2, 2n) = C n /P 2 , the the Grassmanians of 2-planes throught the origin isotropic for a symplectic form, F 4 /P 4 , G 2 /P 1 , E 6 /P 1 , E 6 /P 2 , E 7 /P 1 ,E 7 /P 7 , E 8 /P 8 . Seg(P k × P l ) = A k /P 1 × A l /P 1 . Here we use the ordering of the roots as in [2] .. In all other cases the third fundamental form is easily seen to be nonzero, see [9] . In particular, for all triple and higher Segre products, σ 2 (X) is nondegenerate.. In fact Lickteig and Strassen [11, 12] show many triple Segre products have all secant varieties nondegenerate, in particular for Seg(P n × P n × P n ) the filling secant variety σ r is the expected number r = n 3 /(3n − 2) when n > 3. In particular, for n = m 2 we get roughly m 4 /3 which is significantly greater than m 3 , so in higher dimensions matrix multiplication is far from being a generic tensor. (Lickteig's proof is very simple and elegant -one first observes that certain small cases, e.g., σ 3 (P 1 × P 1 × P n ) fills and then one reduces to such cases by writing a larger vector space as a sum of two dimensional spaces.)

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Supporting network evolution and incremental deployment with XIA eXpressive Internet Architecture (XIA) [1] is an architecture that natively supports multiple communication types and allows networks to evolve their abstractions and functionality to accommodate new styles of communication over time. XIA embeds an elegant mechanism for handling unforeseen communication types for legacy routers.In this demonstration, we show that XIA overcomes three key barriers in network evolution (outlined below) by (1) allowing endhosts and applications to start using new communication types (e.g., service and content) before the network supports them, (2) ensuring that upgrading a subset of routers to support new functionalities immediately benefits applications, and (3) using the same mechanisms we employ for 1 and 2 to incrementally deploy XIA in IP networks.

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Bypass and insertion algorithms for exclusive last-level caches Inclusive last-level caches (LLCs) waste precious silicon estate due to cross-level replication of cache blocks. As the industry moves toward cache hierarchies with larger inner levels, this wasted cache space leads to bigger performance losses compared to exclusive LLCs. However, exclusive LLCs make the design of replacement policies more challenging. While in an inclusive LLC a block can gather a filtered access history, this is not possible in an exclusive design because the block is de-allocated from the LLC on a hit. As a result, the popular least-recently-used replacement policy and its approximations are rendered ineffective and proper choice of insertion ages of cache blocks becomes even more important in exclusive designs. On the other hand, it is not necessary to fill every block into an exclusive LLC. This is known as selective cache bypassing and is not possible to implement in an inclusive LLC because that would violate inclusion. This paper explores insertion and bypass algorithms for exclusive LLCs. Our detailed execution-driven simulation results show that a combination of our best insertion and bypass policies delivers an improvement of up to 61.2% and on average (geometric mean) 3.4% in terms of instructions retired per cycle (IPC) for 97 single-threaded dynamic instruction traces spanning selected SPEC 2006 and server applications, running on a 2 MB 16-way exclusive LLC compared to a baseline exclusive design in the presence of well-tuned multi-stream hardware prefetchers. The corresponding improvements in throughput for 35 4-way multi-programmed workloads running with an 8 MB 16-way shared exclusive LLC are 20.6% (maximum) and 2.5% (geometric mean). Inclusive last-level caches (LLCs) simplify cache coherence protocol; an LLC tag lookup is enough to decide if a cache block is not present in the inner levels of the cache hierarchy. In an exclusive LLC, however, a block is allocated only on an eviction from the inner level cache and de-allocated on a hit when the block is recalled by the inner level cache. As a result, a separate coherence directory array (decoupled from the LLC tag array) is needed to maintain coherence efficiently. While coherence simplification and silent clean evictions from the inner level are seen as major advantages of an inclusive LLC, such a design, by definition, wastes silicon estate due to replication of cached data in multiple levels of the hierarchy. As the industry moves toward a three-level or a four-level cache hierarchy with reasonably large inner levels, such cross-level replication begins to hurt performance in an inclusive design when compared to an exclusive one. This observation has already motivated commercial processor designers to adopt fully or partially exclusive LLCs [1] . The performance gains in an exclusive design over an identical inclusive design usually come from two factors. One of these is the overall capacity advantage enjoyed by the exclusive design. The second performance factor is related to premature evictions in the inner levels of the hierarchy caused by LLC replacements in an inclusive design. In the absence of access hints from the L1 and L2 caches, the last level (L3 in this study) of an inclusive design can end up making wrong replacement decisions [14] . The risk of premature evictions from the L1 and L2 caches triggered by LLC replacements is non-existent in an exclusive design.. In Figure 1 , we show the performance of an exclusive LLC relative to an inclusive LLC for 97 single-threaded dynamic instruction traces representing different regions of floatingpoint SPEC 2006 (FSPEC), integer SPEC 2006 (ISPEC), and server (SERVER) applications with a well-tuned multistream hardware prefetcher enabled. For the left bar, the simulated three-level cache hierarchy in both inclusive and exclusive cases is identical in capacity and associativity at every level. More specifically, the left bar presents simulation results for an architecture with a 512 KB 8-way L2 cache and a 2 MB 16-way LLC. The bar on the right shows the performance of an exclusive LLC relative to an inclusive design, where the exclusive LLC is sized (1.5 MB 12-way) such that the effective capacity advantage of the exclusive design is nullified. In both cases, the inclusive LLC simulates a not-recently-used (NRU) replacement policy (one bit age per block) and the exclusive LLC simulates a onebit not-recently-filled (NRF) replacement policy. The NRU policy victimizes the not recently used block (age zero) from the way with the smallest id. The NRF policy updates the age bit array only on a fill and is otherwise similar to NRU. Both the policies reset the age bits of all the blocks (except the one most recently accessed/filled) in a set to zero only if all blocks in that set have age of one. For each application category, the bar on the right in Figure 1 brings out the performance difference stemming from the premature evictions from the inner levels of the cache hierarchy in the inclusive design. The bar on the left further adds the capacity advantage that an exclusive design enjoys. On average, for 97 traces, the exclusive design enjoys a 3.1% higher IPC than the inclusive design.. While premature LLC replacements can cause performance degradation in inclusive designs, a block resident in the LLC of an inclusive design can still observe a filtered version of access recency during its life time. The situation can further improve with access hints from the inner levels or other proactive mechanisms [14] . This is not possible in an exclusive design. A block resides in the LLC of an exclusive design from the time it is evicted from the L2 cache to the time it is either recalled by the L2 cache or evicted by the LLC, whichever is earlier. Due to the absence of any access information in an exclusive LLC, the popular least-recentlyused (LRU) replacement policy and all its well-researched derivatives lose significance. As a result, the design of replacement policies in an exclusive LLC requires a fresh look. A replacement policy has three distinct algorithmic components, namely, insertion age algorithm, age update algorithm, and victim selection algorithm. In this paper, we explore the insertion age algorithms.. Selective bypass is an important optimization that can be exercised in an exclusive design, since every block evicted from the L2 cache is not required to be filled into the LLC. In an inclusive design, all blocks fetched from memory must be filled in the LLC to maintain inclusion. We explore LLC bypass algorithms in this paper for an exclusive design that can identify clean as well as modified blocks that need not be filled in the LLC. Good LLC bypass policies can improve performance in two ways, namely, by reducing the bandwidth demand of the on-die interconnect as well as the LLC controller and by allocating the LLC capacity only to the blocks with relatively short reuse distances. Figure 2 motivates the two design problems, namely, bypass and insertion in exclusive LLCs, that we explore in this paper. In this figure, we consider a baseline exclusive LLC with NRF replacement policy and no bypass (i.e., all L2 cache evictions are allocated in the LLC). We keep the hardware prefetchers turned off to gain a better understanding of the demand request behavior (we will present results with prefetchers turned on in Section 5). The experiments are conducted on a single-core system with a 2 MB 16-way exclusive LLC. The L2 cache is 512 KB 8-way set associative and instruction and data L1 caches are 16 KB 4-way and 32 KB 8-way set associative, respectively. The L1 and L2 caches execute a pseudo-LRU replacement policy. a) presents the number of LLC misses normalized to the baseline NRF policy for a number of schemes, namely, the popular random replacement with no bypass often used for victim caches (Random), Belady's optimal longest-forward-distance replacement [3, 26] with no bypass (Belady), Belady's optimal replacement extended with bypass which drops an incoming block if its next forward use distance is larger than all the blocks in the target LLC set (Belady-B), and the baseline policy extended with optimal bypass which drops an incoming block if its next forward use distance is larger than the current victim in the target LLC set (Base-B). In this paper, we never bypass instruction blocks. All these experiments are done on an offline cache simulator that has access to the entire LLC allocation/lookup trace. The cache state at the end of warmup is loaded from a checkpoint. The tie between blocks with "unknown" forward distance (next potential use is beyond the trace length) is broken arbitrarily. This work makes the important observation that LRU and its approximations lose meaning in exclusive LLCs and proposes a number of design choices for selective bypassing and insertion age assignment for such designs in a three-level cache hierarchy. Our LLC bypass and age assignment decisions are based on two properties of a block when it is considered for allocation in the LLC. The first one is the number of trips (trip count) made by the block between the L2 cache and the LLC from the time it is brought into the hierarchy till it is evicted from the LLC. The second property is the number of L2 cache hits (use count) experienced by a block during its residency in the L2 cache. Our best proposal is a combination of bypass and age insertion schemes based on These results show that random replacement leads to 4% more LLC misses compared to the baseline policy. On the other hand, Belady, Belady-B, and Base-B show significant potential for improvement. On average, these three schemes save 16%, 16%, and 14% LLC misses.. 2 It is interesting to note that Belady and Belady-B are equally effective meaning that augmenting an already good replacement policy with a bypass decision does not bring any extra advantage in terms of LLC hits. In this case, even though a bypass policy cannot improve the volume of LLC hits, it can save a significant amount of on-die interconnect bandwidth if one could implement a bypass scheme at the L2 cache boundary. It is, however, encouraging to note that a forward-looking bypass scheme working with the NRF policy (Base-B) can save 14% of LLC misses. As expected, the potential for hit rate improvement of a good bypass scheme increases as the replacement policy gets inferior. We, however, make a note of the fact that Base-B comes surprisingly close to Belady and Belady-B, the gap being maximized in the server workloads. We will explain this with the help of Figure 2 (b).. Figure 2(b) shows additional data pertaining to the bypass potential in an exclusive design. For each trace category, Figure 2 (b) shows five different statistics: 1) the number of blocks allocated in the LLC but not used again in the rest of the trace as a fraction of all allocations (Trace-dead), 2) the fraction of blocks allocated in the LLC that are not recalled by the L2 cache before getting evicted from the baseline LLC (LLC-dead-Base), 3) the fraction of blocks allocated in the LLC that are not recalled by the L2 cache before getting evicted from the LLC while executing optimal replacement with no bypass (LLC-dead-Belady), 4) the fraction of all L2 cache evictions bypassed by Belady-B (Belady-B-drop), and 5) the fraction of all L2 cache evictions bypassed by Base-B (Base-B-drop). Among these, the first bar shows the fraction of useless allocations that would have happened in an LLC of infinite capacity. Although this fraction is a direct function of the trace length (longer traces are likely to have smaller values of this fraction), this data emphasizes the facts that the L1 and L2 caches are doing a wonderful job in absorbing all short-term reuses and that most of these reuse clusters are located very far apart. The next bar shows the fraction of useless LLC allocations in the baseline LLC. This is about 75%, on average. This fraction is a realistic representation of the bypass potential. A bypass algorithm should try to make room in the LLC so that a subset of the blocks contributing to the difference of the first two bars can be retained. The third bar shows that even an optimal replacement policy does about 68% of useless allocations in the LLC. This result underscores the importance of a good bypass policy even if the replacement policy is optimal. The fourth bar further confirms this result by showing an equivalent volume of bypasses that an optimal replacement policy with optimal bypass would observe. This result brings to fore the large potential of on-die interconnect bandwidth saving that an LLC bypass policy running at the L2 cache boundary can achieve. Finally, the rightmost bar shows that a forward-looking bypass policy executing with the baseline replacement policy can be as effective as optimal bypass and replacement running together in terms of the fraction of bypassed blocks. We have already noted that the performance gap between Base-B and Belady-B is maximum for the server workloads. This is expected since the bypass fraction is minimum in these workloads leading to the invocation of suboptimal NRF replacement of Base-B for a significant fraction of fills.. Given the large potential in terms of replacement and bypass algorithms, this paper systematically deduces and implements a few such algorithms (Sections 2 and 3). In this study, we explore only the insertion component of the replacement algorithms. Although our bypass algorithms can be seamlessly integrated with the L2 cache, we implement them in the LLC controller and as a result, explore only the capacity benefit of these algorithms. Our detailed executiondriven simulation results (Sections 4 and 5) show that the combination of our best insertion and bypass algorithms improves the IPC of 97 single-threaded traces by up to 61.2% and on average 3.4% on a 2 MB 16-way exclusive LLC compared to the baseline exclusive design with aggressive multistream hardware prefetchers enabled. The corresponding maximum and average improvements in throughput for 35 4-way multi-programmed workloads are 20.6% and 2.5%. In this section, we briefly review the studies that are most relevant to our work. The capacity advantage of exclusive LLCs compared to inclusive LLCs has been studied in [29] , while several techniques to get rid of premature evictions from inner level caches in an inclusive hierarchy have been proposed in [14] . The importance of treating shared blocks specially in an exclusive LLC has been highlighted in [24] . Multi-level exclusive caching in the context of distributed disk caches has been studied in [7] .. Exclusive caches are functionally equivalent to large victim caches [18] . Selective victim caching (analogous to an exclusive LLC with bypass enabled) has been explored in the context of small victim caches that work well with L1 caches [5, 11] . A design of a large victim cache with selective insertion based on frequency of misses has been presented in [2] and is shown to work well with inclusive LLCs. A recent work exploits the dead blocks in an inclusive LLC to configure an "embedded" victim cache [21] .. Dead block prediction schemes [11, 19, 21, 22, 23, 25] have close connection with our bypass proposal. Most of the existing dead block prediction schemes select a dead block in a cache set either for replacement or as a target of a prefetch after the block has spent some time in the cache. These proposals usually correlate the instruction address and/or data address with the death of a cache block. A recent proposal shows how to design an address-oblivious dead block predictor that exploits the reuse probabilities to improve the replacement decisions in an inclusive LLC [4] . On the other hand, our bypass algorithms identify a block that would be dead-on-fill in the LLC at the time of fill. While instruction or data address can improve the quality of bypass, our bypass algorithms do not rely on any such information.. A few recent proposals have explored bypass algorithms for LLCs.. 3 One proposal [6] remembers the tag of a bypassed block (if the incoming block is bypassed) or the victimized block (if the incoming block is not bypassed) to observe the next use to the bypassed/allocated block and the saved/victimized block, and accordingly learns whether bypassing is a good decision. However, this proposal randomly selects incoming blocks for bypassing based on a bypass probability, which is adjusted dynamically based on the effectiveness of bypassing. Another proposal [19] shows how to use a program counter (PC)-based skewed dead block predictor that learns the caching behavior of a few sample sets in the LLC to identify blocks that are dead-on-fill and bypass such blocks. Access counter-based LLC bypass algorithms that take help of a prediction table indexed by a hash function of the PC are explored in [22] . Our bypass algorithms do not require separate prediction tables or any PC-related information, but exploit the reuse frequency that a block sees while in the L2 cache and the number of times it has traveled between the L2 cache and the exclusive LLC. It is important to note that bypass algorithms have also been studied in the context of small data caches.. These proposals require a profile pass that gathers the locality information [17] , or build a PC and data address-based locality predictor [8] , or carry out an instruction-based characterization of the potential of data cache bypassing [28] , or employ a classification of data cache misses into capacity or conflict to drive the bypass decision [5] . Our proposal does not require any profile run or any PC/address/instruction information or miss classification.. There have been several recent studies on insertion age selection for LLCs. Some of these studies require PC information of the source instruction of a to-be-filled block [9, 13] . Also, several of these studies usually identify the insertion age with LRU, MRU, or other access recency positions in a set [9, 13, 16, 20, 27] . As a result, these proposals get tied to the notion of an access recency order, which is nonexistent in an exclusive cache (in the absence of any extra information, the only meaningful order among the blocks in an exclusive cache set is the fill order). A recent study assigns insertion age based on re-reference interval prediction and updates the predicted age on a hit in an inclusive LLC [15] . Although such an option of age update is nonexistent in an exclusive LLC, we will show how to design somewhat analogous policies for exclusive LLCs. A decision tree-based technique for selecting the insertion age relative to the access recency order has been explored in [20] . Our insertion policy proposals are necessarily independent of access recency order.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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Ubiquitous computing using SIP In the past decade, there have been numerous efforts in ubiquitous computing, making computational resources or communication more widely available. We believe that it is time to move to a global-scale ubiquitous computing system that is securable, administered by multiple independent administrators and integrates off-the-shelf hardware and software. We are developing such a system based on the Session Initiation Protocol (SIP), with Bluetooth devices for location sensing and Service Location Protocol (SLP) for service discovery. We also introduce context-aware location information to augment device discovery and user communication.The system builds on our CINEMA infrastructure and can support a range of activities, from home-based settings to collaboration between distant sites. -694-3/03/0006 ...$5.00. administrators and operators and integrate off-the-shelf hardware and software. Thus, scaling requires more than just having a large number of systems.We are developing such a scalable ubiquitous communications and computing system. The system incorporates core tenets of ubiquitous, pervasive and context-aware computing, in particular:Multimedia: We believe that communications incorporates all types of media, from continuous media to application sharing, and we consider multimedia support a core component of a ubiquitous computing environment.Device integration: Our system integrates mobile devices such as programmable active badges, PDAs and laptops with resources embedded into the environment, such as large displays, video projectors, high-resolution video cameras, loudspeakers, stereos and lights. Active multimedia sessions can be moved from one device to another and can be split across devices, so that a multimedia conferencing session might be controlled by a PDA, video shown on a wall-hanging plasma display and audio acquired through an echo-canceling microphone, each with its own network interface.We consider that events offer a useful abstraction for tying together diverse systems while requiring modest knowledge about their properties. We chose the SIP event model [29] as a core component of our system, as it scales to large numbers of users spread across administrative domains.Location is one of the key contexts that determines the types of devices that are available and how communication should be conducted to minimize disruption to the user. Rather than just providing geographic location information, we add higher-level information that describes the category of a place, such as "theater" or "public transport" and its properties (Section 3.2). Other user context, such as the number of people in a room, active conversations or how recently a device has been used, also influence system behavior.We aim to give users maximum control over their incoming communication and the amount of information about their context that is revealed to others.Wherever possible, we delegate system behavior to user-defined policies rather than requiring direct user interaction. Policies can be generated dynamically by presence and location information.The system is designed to support a range of activities, from home-based settings to collaboration between distant sites. It is Ubiquitous computing aims to "enhance computer use by making many computers available throughout the physical environment, but making them effectively invisible to the user." [40] In the past decade, this goal has been pursued in a large number of prototypes [15] , making computational resources or communication more widely available. We believe that it is time to move from special-purpose, one-of-a-kind systems to more widely deployable systems that scale to the global Internet. Such global-scale ubiquitous computing systems need to be securable, administered by multiple, independent * Authors listed in alphabetic order designed so that participation only requires standard SIP-speaking tools such as sipc [38] or Microsoft Windows Messenger or even a basic cell or landline phone. Our system derives its scalability from the underlying SIP architecture. This paper describes workin-progress; we have implemented some of the core ideas and outline others below. It builds on our Columbia InterNet Extensible Multimedia Architecture (CINEMA) infrastructure for multimedia collaboration [18] .. CINEMA is a set of SIP-based Internet Multimedia servers for creating an enterprise Internet telephony and multimedia system. The core part of CINEMA is a SIP proxy, redirect, presence and registration server, named sipd, which can execute service scripts, such as Call Processing Language (CPL) scripts [20] [21] [42] , SIP servlets [28] , and SIP CGI scripts [22] to perform call control services, such as follow-me and call screening. CINEMA also contains a SIP conference server and a SIP voicemail/unified messaging server.. The remainder of the paper is organized as follows. Section 2 discusses earlier research in the area. Section 3 shows our system architecture and explain how we determine and handle location information. Following that, we talk about our current prototype implementation in Section 4. Section 5 presents our service scenario and explain the architectural components. Finally, we conclude this paper in Section 6. We have presented a global scale ubiquitous computing architecture based on open standards like SIP and SLP. We also showed how location information can be acquired in our system and how the information is used to augment end-system capabilities and change device behavior using location aware user preferences. We have validated parts of our architecture through a prototype implementation using the CINEMA system. We will propose our extended location information for standardization as part of MLP and further our development on location-aware automated services by enhancing service-creation languages such as CPL and LESS with location-awareness. The field of ubiquitous computing has provided some very motivating work over the past few years. Some examples are the Intelligent Room (MIT) [5] , the Interactive Workspaces Project (Stanford University) [4] , the Aura Project (CMU) [12] , the Composable ad hoc location-based services [16] and the Easy Living (Microsoft) project [6] , to name a few. While these projects have successfully built systems that effectively interact with the user and the environment, they use proprietary systems and are primarily based on non-standard protocols and are generally limited to a single organization or building. The work presented in this paper is centered around open protocol standards like SIP, SLP [13] and Bluetooth technology and on-going efforts in the IETF.. Some of the work that has been incorporated into our system has been the work of Roy Want and others [39] on active badge location systems. This work introduced the idea of using a variety of active badges developed for location sensing of people and devices. We use an infra-red and radio variation on our active badges as part of authenticating users with the CINEMA system (Section 3.1).. Location based services have received a lot of attention by wireless providers and are integrated into the 3GPP (UMTS) service architecture and WAP [23] .. A related piece of work to the one presented in this paper was proposed by Pospichil et al [27] but deals only with push-based applications and therefore users need to explicitly subscribe to services which take advantage of location information.. The Local Location Assistant (Lol@ [1] ) offers a template for location-based services in UMTS networks. Lol presents a reference implementation for a local location assistant based on a UMTS network.. There are a number of efforts currently underway for establishing a standard for positioning techniques and a standard for relaying location information. Proposals are offered by the Location Inter-operability Forum (LIF) under the Mobile Location Protocol [25] and the Open GIS Consortium. The GEOPRIV working group in the IETF deals primarily with location-dependent privacy issues. Civil and categorical presence information has also been proposed, by one of the authors, as part of the Rich Presence Information Data Format for SIP (RPIDS) [35] and as part of the DHCP option for civil location [34] .

B I O B O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O B O O O O O O O O O O O O O O O O O O B O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O


Motion Tuned Spatio-Temporal Quality Assessment of Natural Videos Abstract-There has recently been a great deal of interest in the development of algorithms that objectively measure the integrity of video signals. Since video signals are being delivered to human end users in an increasingly wide array of applications and products, it is important that automatic methods of video quality assessment (VQA) be available that can assist in controlling the quality of video being delivered to this critical audience. Naturally, the quality of motion representation in videos plays an important role in the perception of video quality, yet existing VQA algorithms make little direct use of motion information, thus limiting their effectiveness. We seek to ameliorate this by developing a general, spatio-spectrally localized multiscale framework for evaluating dynamic video fidelity that integrates both spatial and temporal (and spatio-temporal) aspects of distortion assessment. Video quality is evaluated not only in space and time, but also in space-time, by evaluating motion quality along computed motion trajectories. Using this framework, we develop a full reference VQA algorithm for which we coin the term the MOtion-based Video Integrity Evaluation index, or MOVIE index. It is found that the MOVIE index delivers VQA scores that correlate quite closely with human subjective judgment, using the Video Quality Expert Group (VQEG) FRTV Phase 1 database as a test bed. Indeed, the MOVIE index is found to be quite competitive with, and even outperform, algorithms developed and submitted to the VQEG FRTV Phase 1 study, as well as more recent VQA algorithms tested on this database. Mathematically simple error indices such as the Mean Squared Error (MSE) are often used to evaluate video quality, mostly due to their simplicity. It is well known that the MSE does not correlate well with visual quality, which is the reason why research into full reference VQA techniques has been intensely studied [18] ; see [19] for a review of VQA. Several types of weighted MSE and Peak Signal to Noise Ratio (PSNR) have also been proposed by researchers; see, for example, [20] - [22] .. A substantial amount of the research into IQA and VQA has focused on using models of the HVS to develop quality indices, which we broadly classify as HVS-based indices. The basic idea behind these approaches is that the best way to predict the quality of an image or video, in the absence of any knowledge of the distortion process, is to attempt to "see" the image using a system similar to the HVS. Typical HVS-based indices use linear transforms separably in the spatial and temporal dimensions to decompose the reference and test videos into multiple channels, in an attempt to model the tuning properties of neurons in the front-end of the eye-brain system. Contrast masking, contrast sensitivity and luminance masking models are then used to obtain thresholds of visibility for each channel. The error between the test and reference video in each channel is then normalized by the corresponding threshold to obtain the errors in Just Noticeable Difference (JND) units. The errors from different channels at each pixel are then combined, using the Minkowski error norm or other pooling strategies, to obtain a space-varying map that predicts the probability that a human observer will be able to detect any difference between the two images.. Examples of HVS-based image quality indices include [23] - [27] ; see [28] for a review. It is believed that two kinds of temporal mechanisms exist in the early stages of processing in the HVS, one lowpass and one bandpass, known as the sustained and transient mechanisms [29] , [30] . Most HVS-based video quality indices have been derived from still image quality indices by the addition of a temporal filtering block to model these mechanisms. Popular HVS-based video quality indices such as the Moving Pictures Quality Metric (MPQM) [31] , Perceptual Distortion Metric (PDM) [32] and the Sarnoff JND vision model [24] filter the videos using one bandpass and one lowpass filter along the temporal dimension. Other methods such as the Digital Video Quality (DVQ) metric [33] and the scalable wavelet based video distortion index in [34] utilize a single low pass filter along the temporal dimension. A VQA algorithm that estimates spatiotemporal distortions through a temporal analysis of spatial perceptual distortion maps was presented in [6] .. One of the visual processing tasks performed by the HVS is the computation of speed and direction of motion of objects using the series of time-varying images captured by the retina. All the indices mentioned above use either one or two temporal channels and model the temporal tuning of only the neurons in early stages of the visual pathway such as the retina, lateral geniculate nucleus (LGN) and Area V1 of the cortex. This is the first stage of motion processing that occurs in primate vision systems, the outputs of which are used in latter stages of motion processing that occur in Area MT/V5 of the extra-striate cortex [35] . Visual area MT is believed to play a role in integrating local motion information into a global percept of motion, guidance of some eye movements, segmentation and structure computation in 3-D space [36] . Models of processing in MT is hence essential in VQA due to the critical role of these functions in the perception of videos by human observers. The response properties of neurons in Area MT/V5 are well studied in primates and detailed models of motion sensing have been proposed [37] - [39] . To our knowledge, no VQA index has attempted to incorporate these models to account for visual processing of motion in Area MT.. More recently, there has been a shift toward VQA techniques that attempt to characterize features that the human eye associates with loss of quality; for example, blur, blocking artifacts, fidelity of edge and texture information, color information, contrast and luminance of patches and so on. Part of the reason for this shift in paradigm has been the complexity and incompleteness of models of the HVS. A more important reason, perhaps, is the fact that HVS based models typically model threshold psychophysics, i.e., the sensitivity of the HVS to different features are measured at the threshold of perception [10] , [40] , [41] . However, while detection of distortions is important in some applications, VQA deals with supra-threshold perception, where artifacts in the video sequences are visible and algorithms attempt to quantify the annoyance levels of these distortions. Popular VQA algorithms that embody this approach include the Video Quality Metric (VQM) from NTIA [42] , the SSIM index for video [4] , [5] , Perceptual Video Quality Measure (PVQM) [43] and other algorithms from industry [44] - [48] . However, these models also predominantly capture spatial distortions in the video sequence and fail to do an adequate job in capturing temporal distortions in video. VQM considers 3-D spatio-temporal blocks of video in computing some features, and the only temporal component of the VQM method involves frame differences [42] . The extensions of the SSIM index for video compute local spatial SSIM indices at each frame of the video sequence and use motion information only as weights to combine these local quality measurements into one single quality score for the entire video [4] , [5] . TetraVQM is a VQA algorithm that appeared subsequent to early submissions of this work, that utilizes motion estimation within a VQA framework, where motion compensated errors are computed between the reference and distorted images [7] .. There is a need for improvement in the performance of objective quality indices for video. Most of the indices proposed in the literature have been simple extensions of quality indices for images. Biological vision systems devote considerable resources to motion processing. Presentations of video sequences to human subjects induce visual experiences of motion and the perceived distortion in video sequences is a combination of both spatial and motion artifacts. We argue that accurate representation of motion in video sequences, as well as of temporal distortions, have great potential to advance video quality prediction. We present such an approach to VQA in this paper.

O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O


Constructing a Tree from Homeomorphic Subtrees, with Applications to Computational Evolutionary Biology Abstract. We are given a set T = {T 1 , T 2 , . . . , T k } of rooted binary trees, each T i leaf-labeled by a subset L(T i ) ⊂ {1, 2, . . . , n}. If T is a tree on {1, 2, . . . , n}, we let T |L denote the minimal subtree of T induced by the nodes of L and all their ancestors. The consensus tree problem asks whether there exists a tree T * such that, for every i, T * |L(T i ) is homeomorphic to T i .We present algorithms which test if a given set of trees has a consensus tree and if so, construct one. The deterministic algorithm takes time min{O(N n 1/2 ), O(N + n 2 log n)}, where N = i |T i |, and uses linear space. The randomized algorithm takes time O(N log 3 n) and uses linear space. The previous best for this problem was a 1981 O(N n) algorithm by Aho et al. Our faster deterministic algorithm uses a new efficient algorithm for the following interesting dynamic graph problem: Given a graph G with n nodes and m edges and a sequence of b batches of one or more edge deletions, then, after each batch, either find a new component that has just been created or determine that there is no such component. For this problem, we have a simple algorithm with running time O(n 2 log n + b 0 min{n 2 , m log n}), where b 0 is the number of batches which do not result in a new component. For our particular application, b 0 ≤ 1. If all edges are deleted, then the best previously known deterministic algorithm requires time O(m √ n) to solve this problem. We also present two applications of these consensus tree algorithms which solve other problems in computational evolutionary biology.

O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B I


Encounter-based worms: analysis and defense An encounter-based network is a frequently disconnected wireless ad hoc network requiring immediate neighbors to store and forward aggregated data for information disseminations. Using traditional approaches such as gateways or firewalls to deter worm propagation in encounter-based networks is inappropriate. We propose a worm interaction approach that relies upon automated beneficial worm generation to alleviate problems of worm propagations in such networks. To understand the dynamics of worm interactions and their performance, we mathematically model worm interactions based on major worm interaction factors, including worm interaction types, network characteristics, and node characteristics using ordinary differential equations and analyze their effects on our proposed metrics. We validate our proposed model using extensive synthetic and trace-driven simulations. We find that all worm interaction factors significantly affect the pattern of worm propagations. For example, immunization linearly decreases the infection of susceptible nodes, while on-off behavior only impacts the duration of infection. Using realistic mobile network measurements, we find that encounters are ''bursty'', multi-group, and non-uniform. The trends from the trace-driven simulations are consistent with the model, in general. Immunization and timely deployment seem to be most effective in countering worm attacks in such scenarios, while cooperation may help in a specific case. These findings provide insight that we hope would aid in the development of counter-worm protocols in future encounter-based networks. Most work on worm propagation have focused on modeling single worm type in well connected wired network [3] . However, many worms are shifting their territory to the wireless mobile phone. The characteristics of worms in mobile networks are different from random-scan network worms. Worms in mobile networks depend on user encounter pattern. Many of those worms rely on Bluetooth to broadcast their replications to vulnerable phones, e.g. Cabir and ComWar.M [6] . Since Bluetooth radios have very short range e.g. 10-100 meters, hence, the worms need neighbors in close proximity to spread out their replications. This spreading pattern is very similar to spread of packet replications in encounter-based networks [2, 4] i.e. flooding the copies of messages to all close neighbors. An earlier study in encounter-based networks actually used the term "epidemic routing" [7] to describe the similarity of this routing protocol to disease spreading.. Using traditional approaches such as gateways or firewalls for worm propagation in encounter-based networks is inefficient. Because this type of network is highly dynamic and has no specific boundary, we need a fully distributed security response mechanism. We propose the worm interaction approach that relies upon automated beneficial worm generation [1] . This approach uses an automatic generated beneficial worm to terminate malicious worms and patch the vulnerable hosts to prevent reinfection from malicious worms. We define this type of worm interaction as aggressive one-sided interaction [5] . Before we can use this approach at full potential, we need to understand the worm interaction in this environment. To achieve this goal, we choose to model such worm behavior mathematically. We call this set of equations "aggressive one-sided interaction model".

O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O B B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Fast and stable explicit operator splitting methods for phase-field models Numerical simulations of phase-field models require long time computations and therefore it is necessary to develop efficient and highly accurate numerical methods. In this paper, we propose fast and stable explicit operator splitting methods for both one-and two-dimensional nonlinear diffusion equations for thin film epitaxy with slope selection and Cahn-Hilliard equation. The equations are split into nonlinear and linear parts. The nonlinear part is solved using a method of lines together with an efficient large stability domain explicit ODE solver. The linear part is solved by a pseudo-spectral method, which is based on the exact solution and thus has no stability restriction on the time-step size. We demonstrate the performance of the proposed methods on a number of one-and two-dimensional numerical examples, where different stages of coarsening such as the initial preparation, alternating rapid structural transition and slow motion can be clearly observed. Phase-field models have been recently introduced to describe interfacial phenomena. They were originally derived for the microstructure evolution and phase transition, but have been recently extended to many other physical phenomena, such as solid-solid transitions, growth of cancerous tumors, phase separation of block copolymers, dewetting and rupture of thin liquid films and infiltration of water into porous medium.. Two of these phase-field models have attracted much attention: the molecular beam epitaxy (MBE) equation with slop selection u t = −δ∆ 2 u + ∇ · f (∇u), (x, y) ∈ Ω ⊂ R 2 , t ∈ (0, T ], (1.1) and the Cahn-Hilliard (CH) equation. In this paper, we consider f (ϕ) = ϕ|ϕ| 2 − ϕ, for which the two phase-field models (1.1) and (1.2) become u t = −δ∆ 2 u + ∇ · (|∇u| 2 ∇u − ∇u), (x, y) ∈ Ω ⊂ R 2 , t ∈ (0, T ], (1.3) and u t = −δ∆ 2 u + ∆(u 3 − u), (x, y) ∈ Ω ⊂ R 2 , t ∈ (0, T ].. (1.4). In (1.3), u is a scaled height function of epitaxial growth of thin films in a co-moving frame and the parameter δ is a positive surface diffusion constant. In (1.4), u represents the concentration of one of the two metallic components of the alloy, and the positive parameter δ represents the interfacial width, which is small compared to the characteristic length of the laboratory scale. An important feature of these two equations is that they can be viewed as the gradient flow of the following energy functionals: for the CH one. As it has been shown in [4, 13] , both energy functionals decay in time:. E(u(t)) ≤ E(u(s)), ∀t ≥ s.. Development of highly accurate and efficient numerical methods for (1.3) and (1.4) is a challenging task. Since explicit schemes usually suffer from severe stability restrictions caused by the presence of high-order derivative terms and do not obey the energy decay property, semiimplicit schemes are widely used. In [26] , a combined spectral and large time-stepping method was studied for MBE equation, in which an extra term was added to substantially improve the stability condition. The same method was applied to the CH equation in [11] . However, this artificial stabilization term depends on the unknown numerical solutions and if it is taken improperly, the resulting numerical scheme would be unstable. In [19] , unconditionally energy stable finite-difference schemes were introduced and adaptive time-stepping strategy was proposed to select time-steps adaptively based on the time variation of the energy. This technique was also successfully applied in the simulations of the CH equation in [27] .. In this paper, we develop accurate, efficient and robust explicit methods for both (1.3) and (1.4) subject to periodic boundary conditions. Our methods, which are described in details in §2 and §3, are based on the large stability domain explicit Runge-Kutta methods [2, 3, 12, 16] and the fast explicit operator splitting method proposed in [5, 6, 8, 9 ] (see also [7] ) in the context of convection-diffusion equations.. Following the approach in [5, 6, 8, 9] , we split equation (1.3) into the nonlinear,. and linear, u t = −∆u − δ∆ 2 u (1. 8) parts. We denote by S N the exact solution operator associated with (1.7) and by S L the exact solution operator associated with (1.8) . Notice that the corresponding energy functionals, decay. Then, introducing a (small) splitting step ∆t, the solution of the original equation (1. 3) (which is assumed to be available at time t) is evolved using the Strang splitting method [14, 15, 22] , one step of which can be written as. A similar splitting approach is applied to equation (1.4), for which the linear part is still (1.8) and the nonlinear one is. As in the case of the MBE equation, the corresponding energy functionals,. decay. We stress that even though the linear parts of equations (1.3) and (1.4) are the same, the functionals (1.10) and (1.13) are different since they are associated with the corresponding parts of the energy functionals (1.5) and (1.6). In order to implement the splitting method, the exact solution operators S N and S L have to be replaced by their numerical approximations. Note that one of the main advantages of the operator splitting technique is the fact that the nonlinear, (1.7) and (1.11), and linear, (1.8), subproblems, which are of different nature, can be solved numerically by different methods. First, using the method of lines, (1.7) and (1.11) can be reduced to systems of ODEs, which can be efficiently and accurately integrated by large stability domain explicit ODE solvers [2, 3, 12, 16] . Second, since (1.8) is linear, one can solve it (practically) exactly using, for example, the pseudo-spectral method. This way, no stability restrictions on solving (1.8) are imposed. A detailed description of an efficient implementation of the proposed fast and stable explicit operator splitting methods is given in §2 and §3.. The paper is organized as follows. In §2, we build 2mth-order semi-discrete finite-difference schemes for (1.7) and (1.11). The resulting stiff system of ODE is then solved by an efficient large stability domain explicit ODE solver [1, 17] . In §3, we develop a pseudo-spectral method for the linear equation (1.8) . In §5, we demonstrate the performance of the proposed fast and stable explicit operator splitting methods on a number of one-(1-D) and two-dimensional (2-D) numerical examples, where different stages of coarsening such as the initial preparation, alternating rapid structural transition and slow motion can be clearly observed.. 2 Finite-Difference Methods for (1.7) and (1.11). In this section, we propose efficient explicit finite-difference methods for the degenerate parabolic equations (1.7) and (1.11). These methods are based on the semi-discretization of (1.7) and (1.11) followed by the use of an efficient and accurate ODE solver. The ODE solver will be utilized to evolve the solutions of (1.7) and (1.11) from time t to t + ∆t. We note that in a general case the time-steps of the ODE solver denoted by ∆t ODE will be smaller than the splitting step ∆t so that the approximation of S N (∆t) will typically require several ∆t ODE steps.

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Outage capacities and optimal power allocation for fading multiple-access channels We derive the outage capacity regions of an M-user fading multiple-access channel under the assumption that both the transmitters and the receiver have perfect channel side iriformation. \Ve show t h a t the outage capacity region is implicitly obtained by deriving the outage probability region for a given rate vector. Given the average power constraint and the required rate of each user, we find a successive decoding strategy and a power allocation policy that hound the outage probability region. Also discussed is a simpler minimum common outage prohahility problem under the assumption t h a t the multiple-access channel is either not used a t all when fading is severe or is used simultaneously by all users. Iterative algorithms are proposed for obtaining the optimal decoding order and power allocation in each fading state under the given power constraint of each user. IVireless communication channels vary over time due t o user mobility. By applying optimal dynamic power and rate allocation strategies, the Shannon capacities with channel side information (CSI) at both the transmitter and the receiver of a single-user fading channel, a fading multiple access channel (MAC), and a fading broadcast channel are ohtained in [l] , [2] and [3]. respectively'.. Under the same assumption that CSI is available a t both the transmitter(s) and the receiver(s), the zero-outage capacity regions and the optimal power allocation schemes are derived for the fading MAC and the fading broadcast channel in [4] and [ 5 ] : respectively'. This type of capacity is the maximum instantaneoiis mutual information rate that can be maintained in all fading conditions through optimal power control. By alloning some transmission outage under severe fading conditions. the maximum mutual information rate t h a t can he kept constant during non-outage will increase. Finding the optimal power allocation that achieves the outage capacity for a given outage probahilit? is tantamount t o deriving the power allocation strategy that minimizes the outage probability for a given rate or rate vector. In [6] , the rninirniim oiitagc: prot)abiIit,y prohlem is solved for the single-user fading chiiiin(s1. For iiti M-user fading broadcast channel, under t1ifft:rc:nt. i w i i n i p tions about whether the transmission t,o all iisers is t iiriic:tl off simultaneously or indepentlent,ly, t.hc optimal p o w r idlocation strategy t h a t minimizes the common ouf.agr p r o b ability or hounds the the outage probahility rc:giori of tlic, M users is derived in [ 5 ] .. In this paper we derive the oiitagc capacit.y region iintl the optimal power allocation policy for an Af-iiscr fatlirig MAC under similar assumptions a h i t whether the out a g~ declaration from each user is synchronized or not". Tliis problem is solved in [4] for the case of zero-oiitagc. For the general case where the allowed outage probability of each user is larger than zero, we will show that, the oiitagc: capacity region is implicitly obtained by deterriiining, for each given rate vector R, whether there exists an optimal power allocation such that the average outage probability of each user is no larger than his allowed outage prohahility and the required average transmit power of each iisrr for supporting R during non-outage satisfies his given average power constraint. In particular, given the average power constraint of each user and rate vector R, assiiniing that the outage declaration from each user is synchronized, we derive the optimal power allocation t h a t minimizes the common outage probability of the AI users anti ohtain the minimum common outage. probability. Under thc alteriiative assumption that each user can declare an outage during transmission independently, we derive the outage prohability region of the hf users and the corresponding optimal power allocation that achieves the outage probahility region boundary. Under both assumptions. given the allowed outage probability of each user and rate vector R. we also solve the dual prohleni of finding the average power region of the M users required t o support R for the given outage probability of each user.. The remainder of this paper is organized as follows. In Section 2 we present the fading MAC model. In Section 3, the minimum common outage probability and the outage probability region boundary for a given rate vector R along with the corresponding optimal power allocation strategies are derived and the required average power region for sup3The optimal power allocation is conceptually simpler and easier t o analyze when the outage declaratioii from each user is synchronized. l n practice some applications may also require such synchronization.

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An architecture for a wide area distributed system Distributed systems provide sharing of resources and information over a computer network. A key design issue that makes these systems attractive is that all aspects related to distribution are transparent to users. Unfortunately, general-purpose wide area distributed systems that allow users to share and manage arbitrary resources in a transparent way hardly exist. In particular, they generally do not take into account the most important properties that characterize wide area systems: 1) A very large number of users and resources, 2) an inherent latency problem caused by the distance between nodes, 3) heterogeneity due to a variety of underlying operating systems and networks, and 4) involvement of multiple administrative organizations.The research described in this paper is part of the Globe Project (Globe stands for GLobal Object Based Environment). The goal of this project is the design and implementation of a wide area distributed system that provides a convenient programming abstraction and full transparency. The main contribution of this paper is the description of a new system for distributed shared objects. In contrast to other systems, the implementation of distribution, consistency, and replication of state is completely encapsulated in a distributed shared object. This allows for object-specific solutions, and provides the right mechanism for building efficient and truly scalable systems.

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