MoClo Planner is an interactive visualization system for collaborative bio-design, utilizing a mu... more MoClo Planner is an interactive visualization system for collaborative bio-design, utilizing a multi-touch interactive surface. The system integrates the information gathering, design, and specification of complex synthetic biological constructs using the Modular Cloning (MoClo) assembly method. Modular Cloning is a hierarchical DNA construction method that allows for the assembly of multi-part constructs from a library of biological parts in a one-pot reaction. This cutting-edge method facilitates and expedites the assembly of complex biological designs. However, it is an intricate multi-step process, which to date, has not been adequately supported by existing bio-design tools. Novel visual tools are needed in order to make MoClo more tractable and accessible to a broad range of users, to facilitate a less error prone bio-design process, and to improve workflow. MoClo Planner is a result of a participatory and user-centered design process, which included close collaboration with domain experts. Using multi-touch interactions and a rich graphical interface, the system accelerates the MoClo learning process, and reduces design time and errors. In this paper, we present user requirements and describe the design, implementation, and evaluation of MoClo Planner.
Pigeon is a Web-based tool that translates a textual description of a synthetic biology design in... more Pigeon is a Web-based tool that translates a textual description of a synthetic biology design into an image. It allows programmatic generation of design visualizations, is easy to learn, is easily extensible to new glyphs and notation, and can be connected to other software tools for visualizing their output. We present the Pigeon syntax, its current command set, and some examples of Pigeon programs and their output. KEYWORDS: visualization, software ■ MOTIVATION As synthetic biology matures, it will need software tools to manage information complexity. Modeling and assembly tools apart, there is also a need for tools for communicating designs among synthetic biologists. Visual languages, syntax and semantics governing visual signs and their relationships, have proven to be useful in describing complex designs in many engineering disciplines. A visual sign system is especially useful in synthetic biology because it enables more effective communication and querying of sequence properties important to design and debugging such as adjacency, orientation, order, contiguity, and repetition, than nonvisual descriptions. A de facto visual sign system exists in synthetic biology and is heavily used for manually prototyping designs, and in describing their final form in publication. Such manual methods of visual description, however, are cumbersome, often incomplete or ambiguous, unscalable to larger designs and their many variants, variable across design communities, computer incomprehensible, and are inevitably repeated with generic illustration tools. To alleviate some of these shortcomings, we present a design visualization tool for synthetic biology called Pigeon.
Genetic circuits engineered for mammalian cells often require extensive fine-tuning to perform th... more Genetic circuits engineered for mammalian cells often require extensive fine-tuning to perform their intended functions. To overcome this problem, we present a generalizable biocomputing platform that can engineer genetic circuits which function in human cells with minimal optimization. We used our Boolean Logic and Arithmetic through DNA Excision (BLADE) platform to build more than 100 multi-input-multi-output circuits. We devised a quantitative metric to evaluate the performance of the circuits in human embryonic kidney and Jurkat T cells. Of 113 circuits analysed, 109 functioned (96.5%) with the correct specified behavior without any optimization. We used our platform to build a three-input, two-output Full Adder and six-input, one-output Boolean Logic Look Up Table. We also used BLADE to design circuits with temporal small molecule-mediated inducible control and circuits that incorporate CRISPR/Cas9 to regulate endogenous mammalian genes.
We derive a closed-form expression for the message collision probability in the IEEE 802.3ah Ethe... more We derive a closed-form expression for the message collision probability in the IEEE 802.3ah Ethernet Passive Optical Network (EPON) registration scheme. The expression obtained, although based on an approximation, shows a good match with simulation results. We use the results of our analysis to compute the size of the most efficient contention window and the most efficient number of nodes serviced by a given window size.
IEEE MILCOM 2004. Military Communications Conference, 2004.
As wireless ad hoc networks grow in size and complexiv, the need to study and comprehend the scal... more As wireless ad hoc networks grow in size and complexiv, the need to study and comprehend the scalability and behavior of these systems and their protocol components becomes essential. This paper presents a comprehensive study on the performance of common MANET (mobile ad hoc network) routing protocols in large-scale networks. The routing protocols used in this study include AODV, DSR, OLSR, and ZRP, which represents a good mix of reactive, proactive and hybrid protocols. lNTRODUCTION Mobile ad hoc networks are networks without a fixed infrastructure. Communications must be set up and maintained on the fly over mostly wireless links. Each node of an ad hoc network can both route and forward data. The exploding demand for computing and communication on the move has led to reliance for ad hoc networks. Atthough substantial research efforts have been devoted towards the design and development of ad hoc routing protocols, there is relatively little understanding of their behavior as the system is scaled up. First, it is unclear that any existing ad hoc routing protocol can be used to successfully route data over the many hops that will be necessary in large scale wireless networks. Second, it is unknown which of the preceding techniques is likely to perform better for different types of traffic or mobility patterns as network size grows. This lack of understanding comes from the fact that: previous simulation tools were not able to facilitate the analysis of large scale networks without compromising the fidelity, and thus the accuracy, of the ad hoc network models. Our definition of scalability is that the routing protocoi must provide applications with high throughput and low end-to-end delay, relative to the network scenario. Furthermore, the routing protocol itself must we minimat routing control overhead and exhibit high packet delivery ratio (which correlates to high application throughput). Finally, for a routing protocol to be considered completely scalable, these characteristics must hold true regardless of the network size, node density, number of hops, mobility, Michael J. Acrkhe US ARMY RDECOM CERDEC STCD degrade gracefully if the network configuration has insufficient resources.
Persistent data storage is the basis of all modern information systems. The long-term value and v... more Persistent data storage is the basis of all modern information systems. The long-term value and volume of data are growing at an accelerating rate and pushing extant storage systems to their limits. DNA offers exciting potential as a storage medium, but no practical scheme has been proposed to date that can scale beyond narrow-band write rates. Here, we demonstrate a combinatorial DNA data encoding scheme capable of megabits per second write speeds. The system relies on rapid, combinatorial assembly of multiple smaller DNA parts that are dispensed through inkjet printing. To demonstrate this approach, we wrote approximately 25 kB of information into DNA using our system and read the information back out with commercially available nanopore sequencing. Moreover, we demonstrate the ability to replicate and selectively access the information while it is in DNA, opening up the possibility of more sophisticated DNA computation.
We propose a prefetch cache sizing module for use with any sequential prefetching scheme and eval... more We propose a prefetch cache sizing module for use with any sequential prefetching scheme and evaluate its impact on the hit rate. Disk array caches perform sequential prefetching by loading data contiguous to I/O request data into the array cache. If the I/O workload has sequential locality, then data prefetched in response to sequential accesses in the workload will receive hits. Different schemes prefetch different data, so the prefetch cache size requirement varies. Moreover, the proportion of sequential and random requests in the workload and their interleaving pattern affects the size requirement. If the cache is too small, then prefetched data would get evicted from the cache before a request for the data arrives, thus lowering the hit rate. If the cache is too large, then valuable cache space is wasted. We present a simple sizing module that can be added to any prefetching scheme to ensure that the prefetch cache size is adequately matched to the requirement of the prefetching scheme on a dynamic workload comprising multiple streams. We analytically compute the maximal hit rate achievable by popular prefetching schemes and through simulations, show that our sizing module maintains the prefetch cache at a size that nearly achieves this maximal hit rate.
As WANs continue to form the framework for deploying mission-critical applications, the need for ... more As WANs continue to form the framework for deploying mission-critical applications, the need for fault resilience and fast restoration assumes greater importance. This paper examines existing schemes for fast restoration signaling in a wavelength-routed optical core and introduces an improved signaling scheme based on Optical Burst Switching and Just-Enough-Time path establishment. Scaling experiments show that the proposed scheme outperforms existing schemes.
This report discusses an experiment to discover the optimal amplitude and speed (frequency) of os... more This report discusses an experiment to discover the optimal amplitude and speed (frequency) of oscillation that is most conducive to the perception of depth and 3D-space
Synthetic Biology is an engineering discipline where parts of DNA sequences are composed into nov... more Synthetic Biology is an engineering discipline where parts of DNA sequences are composed into novel, complex systems that execute a desired biological function. Functioning and well-behaving biological sys-tems adhere to a certain set of biological “rules”. Data exchange standards and Bio-Design Automation (BDA) tools support the organization of part libraries and the exploration of rule-compliant compositions. In this work, we formally define a design specification language, enabling the integration of biological rules into the Synthetic Biology engineering process. The supported rules are divided into five categories: Counting, Pairing, Positioning, Orientation, and Interactions. We formally define the semantics of each rule, charac-terize the language’s expressive power, and perform a case study in that we iteratively design a genetic Priority Encoder circuit following two alternative paradigms — rule-based and template-driven. Ultimately, we touch a method to approximate the com...
ABSTRACT: Raising the level of abstraction for synthetic biology design requires solving several ... more ABSTRACT: Raising the level of abstraction for synthetic biology design requires solving several challenging problems, including mapping abstract designs to DNA sequences. In this paper we present the first formalism and algorithms to address this problem. The key steps of this transformation are feature matching, signal matching, and part matching. Feature matching ensures that the mapping satisfies the regulatory relationships in the abstract design. Signal matching ensures that the expression levels of functional units are compatible. Finally, part matching finds a DNA part sequence that can implement the design. Our software tool MatchMaker implements these three steps.
Synthetic biology is an emerging field in which biologists modify or design the behavior of organ... more Synthetic biology is an emerging field in which biologists modify or design the behavior of organisms to engineer systems that perform computation in diverse biological applications. Synthetic biologists design such a complex
Abstract. One of the main appeals of mobile sensors is the variety of environments in which they ... more Abstract. One of the main appeals of mobile sensors is the variety of environments in which they can operate as an autonomous network. Different environments, however, present different challenges, especially in terms of inter-sensor communication. In sparse environments, it may not be possible to maintain full connectivity at all times, setting off the need for agents to communicate opportunistically when they are close to each other. This, in turn, suggests that communication needs be taken into account in the design of agents ’ trajectories. In this paper, we introduce a notion of tour and meeting point as an abstraction of trajectories designed for both sensing and communication, and we study the tradeoffs involved between motion to sense and sample and motion to communicate and interact.
Jacob Beal Ron Weiss Douglas Densmore Aaron Adler Jonathan Babb Swapnil Bhatia Noah Davidsohn Tra... more Jacob Beal Ron Weiss Douglas Densmore Aaron Adler Jonathan Babb Swapnil Bhatia Noah Davidsohn Traci Haddock Fusun Yaman Richard Schantz Joseph Loyall BBN Technologies 10 Moulton Street Cambridge, MA, USA 02138 MIT 77 Massachusetts Ave Cambridge, MA, USA 02139 Boston University 8 Saint Mary’s St. Boston, MA, USA 02215 {jakebeal,fyaman, aadler, rschantz, jloyall}@bbn.com, {rweiss, ndavidso, jbabb}@mit.edu, {dougd,swapnilb,thaddock}@bu.edu
Digital electronic circuits have inspired synthetic biologists to program living cells with synth... more Digital electronic circuits have inspired synthetic biologists to program living cells with synthetic decision-mak- ing circuits by creating multilevel genetic logic gates. In both genetic and electronic circuits, logic synthesis translates an abstract functional description into a representation that can be physically implemented. However, inherent differences in genetic logic devices present new synthesis challenges. Here we provide a starting point for a growing set of biodesign au- tomation tools to tackle this challenge in a unified way. This framework will enable direct comparison of new approaches, results that are transferable and standardized, and research into independent areas of the problem formulation with a clear path toward future integration.
We solve a counting problem proposed by Balas and Connor [1] derive d from a game calledLook Up a... more We solve a counting problem proposed by Balas and Connor [1] derive d from a game calledLook Up and Scream . Our solution applies to both variants of the game and is based on counting matchings of every size in the constraints gr aph of the game. We count such matchings directly in the unconstrained varian t of the game and use a counting technique discovered by J. P. McSorley [2] for the constrained variant. 1 Look Up and Scream Balas and Connor introduce a new game called Look Up and Scream (LUaS) [1]. The game involves2N participants standing in a circle. The game is played in roun ds where each round proceeds as follows: At the beginning of the round, every participant looks down at the floor. Then, on cue, all the participants loo k up simultaneously, and instantaneously choose to fix their gaze on another player. I f any two players realize that they have chosen to gaze at each other, they scream and th e round ends with aloss or failure. A new round is then played. The game e...
TaP is a storage cache sequential prefetching and caching technique to improve the read-ahead cac... more TaP is a storage cache sequential prefetching and caching technique to improve the read-ahead cache hit rate and system response time. A unique feature of TaP is the use of a table to detect sequential access patterns in the I/O workload and to dynamically determine the optimum prefetch cache size. When compared to some popular prefetching techniques, TaP gives a better hit rate and response time while using a read cache that is often an order of magnitude smaller than that needed by other techniques. TaP is especially efficient when the I/O workload consists of interleaved requests from various applications, where only some of the applications are accessing their data sequentially. For example, TaP achieves the same hit rate as the other techniques with a cache length that is 100 times smaller than the cache needed by other techniques when the interleaved workload consists of 10% sequential application data and 90% random application data.
To a storage systems researcher, all user bytes are created opaque and equal. Whether they encode... more To a storage systems researcher, all user bytes are created opaque and equal. Whether they encode a timeless wedding photograph, a recording of a song downloaded from the WWW, or tax returns of yesteryear is not germane to the already complex problem of their storage. But according to Cathy Marshall, this is only one stripe of the storage beast. There is a bigger problem that we will have to confront eventually: The exponentially growing size of our personal digital estate will soon—if it has not done so already—surpass our management abilities.
MoClo Planner is an interactive visualization system for collaborative bio-design, utilizing a mu... more MoClo Planner is an interactive visualization system for collaborative bio-design, utilizing a multi-touch interactive surface. The system integrates the information gathering, design, and specification of complex synthetic biological constructs using the Modular Cloning (MoClo) assembly method. Modular Cloning is a hierarchical DNA construction method that allows for the assembly of multi-part constructs from a library of biological parts in a one-pot reaction. This cutting-edge method facilitates and expedites the assembly of complex biological designs. However, it is an intricate multi-step process, which to date, has not been adequately supported by existing bio-design tools. Novel visual tools are needed in order to make MoClo more tractable and accessible to a broad range of users, to facilitate a less error prone bio-design process, and to improve workflow. MoClo Planner is a result of a participatory and user-centered design process, which included close collaboration with domain experts. Using multi-touch interactions and a rich graphical interface, the system accelerates the MoClo learning process, and reduces design time and errors. In this paper, we present user requirements and describe the design, implementation, and evaluation of MoClo Planner.
Pigeon is a Web-based tool that translates a textual description of a synthetic biology design in... more Pigeon is a Web-based tool that translates a textual description of a synthetic biology design into an image. It allows programmatic generation of design visualizations, is easy to learn, is easily extensible to new glyphs and notation, and can be connected to other software tools for visualizing their output. We present the Pigeon syntax, its current command set, and some examples of Pigeon programs and their output. KEYWORDS: visualization, software ■ MOTIVATION As synthetic biology matures, it will need software tools to manage information complexity. Modeling and assembly tools apart, there is also a need for tools for communicating designs among synthetic biologists. Visual languages, syntax and semantics governing visual signs and their relationships, have proven to be useful in describing complex designs in many engineering disciplines. A visual sign system is especially useful in synthetic biology because it enables more effective communication and querying of sequence properties important to design and debugging such as adjacency, orientation, order, contiguity, and repetition, than nonvisual descriptions. A de facto visual sign system exists in synthetic biology and is heavily used for manually prototyping designs, and in describing their final form in publication. Such manual methods of visual description, however, are cumbersome, often incomplete or ambiguous, unscalable to larger designs and their many variants, variable across design communities, computer incomprehensible, and are inevitably repeated with generic illustration tools. To alleviate some of these shortcomings, we present a design visualization tool for synthetic biology called Pigeon.
Genetic circuits engineered for mammalian cells often require extensive fine-tuning to perform th... more Genetic circuits engineered for mammalian cells often require extensive fine-tuning to perform their intended functions. To overcome this problem, we present a generalizable biocomputing platform that can engineer genetic circuits which function in human cells with minimal optimization. We used our Boolean Logic and Arithmetic through DNA Excision (BLADE) platform to build more than 100 multi-input-multi-output circuits. We devised a quantitative metric to evaluate the performance of the circuits in human embryonic kidney and Jurkat T cells. Of 113 circuits analysed, 109 functioned (96.5%) with the correct specified behavior without any optimization. We used our platform to build a three-input, two-output Full Adder and six-input, one-output Boolean Logic Look Up Table. We also used BLADE to design circuits with temporal small molecule-mediated inducible control and circuits that incorporate CRISPR/Cas9 to regulate endogenous mammalian genes.
We derive a closed-form expression for the message collision probability in the IEEE 802.3ah Ethe... more We derive a closed-form expression for the message collision probability in the IEEE 802.3ah Ethernet Passive Optical Network (EPON) registration scheme. The expression obtained, although based on an approximation, shows a good match with simulation results. We use the results of our analysis to compute the size of the most efficient contention window and the most efficient number of nodes serviced by a given window size.
IEEE MILCOM 2004. Military Communications Conference, 2004.
As wireless ad hoc networks grow in size and complexiv, the need to study and comprehend the scal... more As wireless ad hoc networks grow in size and complexiv, the need to study and comprehend the scalability and behavior of these systems and their protocol components becomes essential. This paper presents a comprehensive study on the performance of common MANET (mobile ad hoc network) routing protocols in large-scale networks. The routing protocols used in this study include AODV, DSR, OLSR, and ZRP, which represents a good mix of reactive, proactive and hybrid protocols. lNTRODUCTION Mobile ad hoc networks are networks without a fixed infrastructure. Communications must be set up and maintained on the fly over mostly wireless links. Each node of an ad hoc network can both route and forward data. The exploding demand for computing and communication on the move has led to reliance for ad hoc networks. Atthough substantial research efforts have been devoted towards the design and development of ad hoc routing protocols, there is relatively little understanding of their behavior as the system is scaled up. First, it is unclear that any existing ad hoc routing protocol can be used to successfully route data over the many hops that will be necessary in large scale wireless networks. Second, it is unknown which of the preceding techniques is likely to perform better for different types of traffic or mobility patterns as network size grows. This lack of understanding comes from the fact that: previous simulation tools were not able to facilitate the analysis of large scale networks without compromising the fidelity, and thus the accuracy, of the ad hoc network models. Our definition of scalability is that the routing protocoi must provide applications with high throughput and low end-to-end delay, relative to the network scenario. Furthermore, the routing protocol itself must we minimat routing control overhead and exhibit high packet delivery ratio (which correlates to high application throughput). Finally, for a routing protocol to be considered completely scalable, these characteristics must hold true regardless of the network size, node density, number of hops, mobility, Michael J. Acrkhe US ARMY RDECOM CERDEC STCD degrade gracefully if the network configuration has insufficient resources.
Persistent data storage is the basis of all modern information systems. The long-term value and v... more Persistent data storage is the basis of all modern information systems. The long-term value and volume of data are growing at an accelerating rate and pushing extant storage systems to their limits. DNA offers exciting potential as a storage medium, but no practical scheme has been proposed to date that can scale beyond narrow-band write rates. Here, we demonstrate a combinatorial DNA data encoding scheme capable of megabits per second write speeds. The system relies on rapid, combinatorial assembly of multiple smaller DNA parts that are dispensed through inkjet printing. To demonstrate this approach, we wrote approximately 25 kB of information into DNA using our system and read the information back out with commercially available nanopore sequencing. Moreover, we demonstrate the ability to replicate and selectively access the information while it is in DNA, opening up the possibility of more sophisticated DNA computation.
We propose a prefetch cache sizing module for use with any sequential prefetching scheme and eval... more We propose a prefetch cache sizing module for use with any sequential prefetching scheme and evaluate its impact on the hit rate. Disk array caches perform sequential prefetching by loading data contiguous to I/O request data into the array cache. If the I/O workload has sequential locality, then data prefetched in response to sequential accesses in the workload will receive hits. Different schemes prefetch different data, so the prefetch cache size requirement varies. Moreover, the proportion of sequential and random requests in the workload and their interleaving pattern affects the size requirement. If the cache is too small, then prefetched data would get evicted from the cache before a request for the data arrives, thus lowering the hit rate. If the cache is too large, then valuable cache space is wasted. We present a simple sizing module that can be added to any prefetching scheme to ensure that the prefetch cache size is adequately matched to the requirement of the prefetching scheme on a dynamic workload comprising multiple streams. We analytically compute the maximal hit rate achievable by popular prefetching schemes and through simulations, show that our sizing module maintains the prefetch cache at a size that nearly achieves this maximal hit rate.
As WANs continue to form the framework for deploying mission-critical applications, the need for ... more As WANs continue to form the framework for deploying mission-critical applications, the need for fault resilience and fast restoration assumes greater importance. This paper examines existing schemes for fast restoration signaling in a wavelength-routed optical core and introduces an improved signaling scheme based on Optical Burst Switching and Just-Enough-Time path establishment. Scaling experiments show that the proposed scheme outperforms existing schemes.
This report discusses an experiment to discover the optimal amplitude and speed (frequency) of os... more This report discusses an experiment to discover the optimal amplitude and speed (frequency) of oscillation that is most conducive to the perception of depth and 3D-space
Synthetic Biology is an engineering discipline where parts of DNA sequences are composed into nov... more Synthetic Biology is an engineering discipline where parts of DNA sequences are composed into novel, complex systems that execute a desired biological function. Functioning and well-behaving biological sys-tems adhere to a certain set of biological “rules”. Data exchange standards and Bio-Design Automation (BDA) tools support the organization of part libraries and the exploration of rule-compliant compositions. In this work, we formally define a design specification language, enabling the integration of biological rules into the Synthetic Biology engineering process. The supported rules are divided into five categories: Counting, Pairing, Positioning, Orientation, and Interactions. We formally define the semantics of each rule, charac-terize the language’s expressive power, and perform a case study in that we iteratively design a genetic Priority Encoder circuit following two alternative paradigms — rule-based and template-driven. Ultimately, we touch a method to approximate the com...
ABSTRACT: Raising the level of abstraction for synthetic biology design requires solving several ... more ABSTRACT: Raising the level of abstraction for synthetic biology design requires solving several challenging problems, including mapping abstract designs to DNA sequences. In this paper we present the first formalism and algorithms to address this problem. The key steps of this transformation are feature matching, signal matching, and part matching. Feature matching ensures that the mapping satisfies the regulatory relationships in the abstract design. Signal matching ensures that the expression levels of functional units are compatible. Finally, part matching finds a DNA part sequence that can implement the design. Our software tool MatchMaker implements these three steps.
Synthetic biology is an emerging field in which biologists modify or design the behavior of organ... more Synthetic biology is an emerging field in which biologists modify or design the behavior of organisms to engineer systems that perform computation in diverse biological applications. Synthetic biologists design such a complex
Abstract. One of the main appeals of mobile sensors is the variety of environments in which they ... more Abstract. One of the main appeals of mobile sensors is the variety of environments in which they can operate as an autonomous network. Different environments, however, present different challenges, especially in terms of inter-sensor communication. In sparse environments, it may not be possible to maintain full connectivity at all times, setting off the need for agents to communicate opportunistically when they are close to each other. This, in turn, suggests that communication needs be taken into account in the design of agents ’ trajectories. In this paper, we introduce a notion of tour and meeting point as an abstraction of trajectories designed for both sensing and communication, and we study the tradeoffs involved between motion to sense and sample and motion to communicate and interact.
Jacob Beal Ron Weiss Douglas Densmore Aaron Adler Jonathan Babb Swapnil Bhatia Noah Davidsohn Tra... more Jacob Beal Ron Weiss Douglas Densmore Aaron Adler Jonathan Babb Swapnil Bhatia Noah Davidsohn Traci Haddock Fusun Yaman Richard Schantz Joseph Loyall BBN Technologies 10 Moulton Street Cambridge, MA, USA 02138 MIT 77 Massachusetts Ave Cambridge, MA, USA 02139 Boston University 8 Saint Mary’s St. Boston, MA, USA 02215 {jakebeal,fyaman, aadler, rschantz, jloyall}@bbn.com, {rweiss, ndavidso, jbabb}@mit.edu, {dougd,swapnilb,thaddock}@bu.edu
Digital electronic circuits have inspired synthetic biologists to program living cells with synth... more Digital electronic circuits have inspired synthetic biologists to program living cells with synthetic decision-mak- ing circuits by creating multilevel genetic logic gates. In both genetic and electronic circuits, logic synthesis translates an abstract functional description into a representation that can be physically implemented. However, inherent differences in genetic logic devices present new synthesis challenges. Here we provide a starting point for a growing set of biodesign au- tomation tools to tackle this challenge in a unified way. This framework will enable direct comparison of new approaches, results that are transferable and standardized, and research into independent areas of the problem formulation with a clear path toward future integration.
We solve a counting problem proposed by Balas and Connor [1] derive d from a game calledLook Up a... more We solve a counting problem proposed by Balas and Connor [1] derive d from a game calledLook Up and Scream . Our solution applies to both variants of the game and is based on counting matchings of every size in the constraints gr aph of the game. We count such matchings directly in the unconstrained varian t of the game and use a counting technique discovered by J. P. McSorley [2] for the constrained variant. 1 Look Up and Scream Balas and Connor introduce a new game called Look Up and Scream (LUaS) [1]. The game involves2N participants standing in a circle. The game is played in roun ds where each round proceeds as follows: At the beginning of the round, every participant looks down at the floor. Then, on cue, all the participants loo k up simultaneously, and instantaneously choose to fix their gaze on another player. I f any two players realize that they have chosen to gaze at each other, they scream and th e round ends with aloss or failure. A new round is then played. The game e...
TaP is a storage cache sequential prefetching and caching technique to improve the read-ahead cac... more TaP is a storage cache sequential prefetching and caching technique to improve the read-ahead cache hit rate and system response time. A unique feature of TaP is the use of a table to detect sequential access patterns in the I/O workload and to dynamically determine the optimum prefetch cache size. When compared to some popular prefetching techniques, TaP gives a better hit rate and response time while using a read cache that is often an order of magnitude smaller than that needed by other techniques. TaP is especially efficient when the I/O workload consists of interleaved requests from various applications, where only some of the applications are accessing their data sequentially. For example, TaP achieves the same hit rate as the other techniques with a cache length that is 100 times smaller than the cache needed by other techniques when the interleaved workload consists of 10% sequential application data and 90% random application data.
To a storage systems researcher, all user bytes are created opaque and equal. Whether they encode... more To a storage systems researcher, all user bytes are created opaque and equal. Whether they encode a timeless wedding photograph, a recording of a song downloaded from the WWW, or tax returns of yesteryear is not germane to the already complex problem of their storage. But according to Cathy Marshall, this is only one stripe of the storage beast. There is a bigger problem that we will have to confront eventually: The exponentially growing size of our personal digital estate will soon—if it has not done so already—surpass our management abilities.
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