After the performance improvement rate in single-core processors decreased in 2000s, most CPU manufacturers have steered towards parallel computing. Parallel computing has been in the spotlight for a while now. Several hardware and software innovations are being examined and developed, in order to improve the efficiency of parallel computing. Signal processing is an important application area of parallel computing, and this makes parallel computing interesting for Ericsson AB, a company that among other business areas, is mainly focusing on communication technologies. The Ericsson baseband research team at Lindholmen, has been developing a small, experimental basic operating system (BOS) for research purposes within the area of parallel computing. One major overhead in parallel applications, which increases the latency in applications, is the communication overhead between the cores. It had been observed that in some signal processing applications, it is common for some tasks of the parallel application to have a large data size but a small code size. The question was risen then, could it be beneficial to move code instead of data in such cases, to reduce the communication overhead. In this thesis work the gain and practical difficulties of moving code are investigated through implementation. A method has been successfully developed and integrated into BOS to move the code between the cores on a multi-core architecture. While it can be a very specific class of applications in which it is useful to move code, it is shown that it is possible to move the code between the cores with zero extra overhead.

In this work, we develop a many-body theory of electronic transport through single molecule junctions based on nonequilibrium Green’s functions (NEGFs). The central quantity of this theory is the Coulomb self-energy matrix of the junction ∑(C). ∑(C) is evaluated exactly in the sequential-tunneling limit, and the correction due to finite lead-molecule tunneling is evaluated using a conserving approximation based on diagrammatic perturbation theory on the Keldysh contour. In this way, tunneling processes are included to infinite order, meaning that any approximation utilized is a truncation in the physical processes considered rather than in the order of those processes. Our theory reproduces the key features of both the Coulomb blockade and coherent transport regimes simultaneously in a single unified theory. Nonperturbative effects of intramolecular correlations are included, which are necessary to accurately describe the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, essential for a quantitative theory of transport. This work covers four major topics related to transport in single-molecule junctions. First, we use our many-body theory to calculate the nonlinear electrical response of the archetypal Au-1,4-benzenedithiol-Au junction and find irregularly shaped ‘molecular diamonds’ which have been experimentally observed in some larger molecules but which are inaccessible to existing theoretical approaches. Next, we extend our theory to include heat transport and develop an exact expression for the heat current in an interacting nanostructure. Using this result, we discover that quantum coherence can strongly enhance the thermoelectric response of a device, a result with a number of technological applications. We then develop the formalism to include multi-orbital lead-molecule contacts and multi-channel leads, both of which strongly affect the observable transport. Lastly, we include a dynamic screening correction to ∑(C) and investigate the optoelectric response of several molecular junctions.

<p>The correctness of a cache coherence protocol is crucial to the system since a subtle bug in the protocol may lead to disastrous consequences. However, the verification of a cache coherence protocol is never an easy task due to the complexity of the protocol. Moreover, as more and more cores are compressed into a single chip, there is an urge for the cache coherence protocol to have higher performance, lower power consumption, and less storage overhead. People perform various optimizations to meet these goals, which unfortunately, further exacerbate the verification problem. The current situation is that there are no efficient and universal methods for verifying a realistic cache coherence protocol for a many-core system. </p><p>We, as architects, believe that we can alleviate the verification problem by changing the traditional design paradigm. We suggest taking verifiability as a first-class design constraint, just as we do with other traditional metrics, such as performance, power consumption, and area overhead. To do this, we need to incorporate verification effort in the early design stage of a cache coherence protocol and make wise design decisions regarding the verifiability. Such a protocol will be amenable to verification and easier to be verified in a later stage. Specifically, we propose two methods in this thesis for designing scalably verifiable cache coherence protocols. </p><p>The first method is Fractal Coherence, targeting verifiable hierarchical protocols. Fractal Coherence leverages the fractal idea to design a cache coherence protocol. The self-similarity of the fractal enables the inductive verification of the protocol. Such a verification process is independent of the number of nodes and thus is scalable. We also design example protocols to show that Fractal Coherence protocols can attain comparable performance compared to a traditional snooping or directory protocol. </p><p>As a system scales hierarchically, Fractal Coherence can perfectly solve the verification problem of the implemented cache coherence protocol. However, Fractal Coherence cannot help if the system scales horizontally. Therefore, we propose the second method, PVCoherence, targeting verifiable flat protocols. PVCoherence is based on parametric verification, a widely used method for verifying the coherence of a flat protocol with infinite number of nodes. PVCoherence captures the fundamental requirements and limitations of parametric verification and proposes a set of guidelines for designing cache coherence protocols that are compatible with parametric verification. As long as designers follow these guidelines, their protocols can be easily verified. </p><p>We further show that Fractal Coherence and PVCoherence can also facilitate the verification of memory consistency, another extremely challenging problem. One piece of previous work proves that the verification of memory consistency can be decomposed into three steps. The most complex and non-scalable step is the verification of the cache coherence protocol. If we design the protocol following the design methodology of Fractal Coherence or PVCoherence, we can easily verify the cache coherence protocol and overcome the biggest obstacle in the verification of memory consistency. </p><p>As system expands and cache coherence protocols get more complex, the verification problem of the protocol becomes more prominent. We believe it is time to reconsider the traditional design flow in which verification is totally separated from the design stage. We show that by incorporating the verifiability in the early design stage and designing protocols to be scalably verifiable in the first place, we can greatly reduce the burden of verification. Meanwhile, we perform various experiments and show that we do not lose benefits in performance as well as in other metrics when we obtain the correctness guarantee.</p> / Dissertation

No description available.

In this study I present two N-body computer simulations of the Bullet Cluster (1E 0657-56) merging system. The models are fully self-consistent, meaning that all gravitational forces are determined by the distribution of the particles. Initial positions and velocities of the two clusters are determined by solving a two-body problem. Post-collision time period shows an increase in the line-of-sight velocity dispersion in both clusters, and is consistent with previous Bullet Cluster studies. I also investigate the temporal evolution of the average cluster radial velocities of the galaxies located in the inner, middle, and outer regions of the clusters. I show that the orbital trajectories differ in pre- and post-collision periods. Inner region galaxies receive an impulse that moves them outward from the cluster center immediately after collision, while at the same time the outer region galaxies are pulled back towards the cluster center. / Department of Physics and Astronomy

This thesis involves the study of a repulsive-attractive N-body problem, which is a subclass of a quasihomogeneous N-body problem [5]. The quasihomogeneous N-body problem is the study of N point masses moving in R3N, where the negative of the potential energy is of the form, X 1≤i<j≤N bmimjr−β ij + X 1≤i<j≤N amimjr−α ij . In the above equation, rij is the distance between the point mass mi and the point mass mj , and a, b, α > β > 0 are constants. The repulsive-attractive N-body problem is the case where a < 0 and b > 0. We start the ground work for the study of the repulsive-attractive N-body problem by defining the first integrals, collisions and pseudo-collisions and the collision set. By examining the potentials where a < 0 and b > 0, we see that the dominant force is repulsive. This means that the closer two point masses get the greater the force acting to separate them becomes. This property leads to the main result of the first chapter: there can be no collisions or pseudo-collisions for any repulsive-attractive system. In the next chapter we study central configurations of the system. Quasihomogeneous potentials will have different central configurations than homogeneous potentials [6], thus requiring the classification of two new subsets of central configurations. Loosely speaking, the set of central configurations that are not central configurations for any homogeneous potential are called extraneous. The set of configurations that are central configurations for both homogeneous potentials that make up the quasihomogeneous potential, are called simultaneous configurations. We also notice that every simultaneous central configuration will be non-extraneous, therefore the two subsets are disjoint. Next we show the existence of oscillating homothetic periodic orbits associated with non-extraneous configurations. Finally in this chapter, we investigate the polygon solutions for repulsive-attractive N-body problems [11]. In particular we show that the masses need no longer to be equal, for repulsive-attractive potentials. It will be shown that there exists a square configuration with m1 = m2 6= m3 = m4, that leads to a relative equilibrium. Therefore, for N = 4 the set of extraneous configurations is non-empty. The last chapter deals with the complete analysis of the generalized Lennard- Jones 2-body problem. The generalized Lennard-Jones problem is the subcase of the repulsive-attractive N-body problem, where a = −1, b = 2, and α = 2β. We proceed as in [13] by using diffeomorphic transforms to get an associated system thereby generating a picture of the global flow of the system. This gives us the complete flow for the generalized Lennard-Jones 2-body problem.

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (leaves 241-264). Also available via World Wide Web.

Dissertation (Ph.D.)--University of Toledo, 2007. / Typescript. "Submitted as partial fulfillment of the requirements for The Doctor of Philosophy Degree in Physics." Bibliography: leaves 87-90.

Thesis (Ph. D.)--Brigham Young Dept. of Mathematics, 2006. / Includes bibliographical references (p. 87-90).

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.