Raw fabric hardware implementation and characterization

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 109-110).The Raw architecture is scalable, improving performance not by pushing the limits of clock frequency, but by spreading computation across numerous simple, replicated tiles. The first Raw processors fabricated have 16 RISC processor tiles that share the workload. The Raw Fabric system extends Raw's scalability by weaving together multiple 16-tile Raw processors. The Raw Fabric is a modular and scalable system comprised of two board types: one to house 4 Raw processors (Processor board) and one to handle communications (I/O board). The design is modular because it breaks down the system into smaller parts, and it is scalable because these modules may be combined to create large Fabrics. The ultimate goal is to produce a Raw Fabric with 16 Processor boards (equivalently, 64 Raw processors or 1024 tiles), though the current largest Fabric system includes one Processor board and 3 I/O boards. This thesis walks through the important design and implementation challenges and documents how they were solved. The most basic challenge faced was to design a system flexible enough to accommodate a variety of Fabric sizes.(cont.) Next, the distribution of vital signals such as power and clock provides a problem unique to the Fabric system because of the possible size of the final product. Finally, the astounding number of signal wires running between boards presents a unique challenge in finding parts and designing the mechanical aspects. The intent of this thesis is to provide the reader with an idea of the considerations necessary for designing and implementing a system of this magnitude and level of flexibility.by Albert Sun.M.Eng

Magnetization reversal by injection and transfer of spin: experiments and theory

Reversing the magnetization of a ferromagnet by spin transfer from a current, rather than by applying a magnetic field, is the central idea of an extensive current research. After a review of our experiments of current-induced magnetization reversal in Co/Cu/Co trilayered pillars, we present the model we have worked out for the calculation of the current-induced torque and the interpretation of the experiments

Hierarchical characterization of complex networks

While the majority of approaches to the characterization of complex networks has relied on measurements considering only the immediate neighborhood of each network node, valuable information about the network topological properties can be obtained by considering further neighborhoods. The current work discusses on how the concepts of hierarchical node degree and hierarchical clustering coefficient (introduced in cond-mat/0408076), complemented by new hierarchical measurements, can be used in order to obtain a powerful set of topological features of complex networks. The interpretation of such measurements is discussed, including an analytical study of the hierarchical node degree for random networks, and the potential of the suggested measurements for the characterization of complex networks is illustrated with respect to simulations of random, scale-free and regular network models as well as real data (airports, proteins and word associations). The enhanced characterization of the connectivity provided by the set of hierarchical measurements also allows the use of agglomerative clustering methods in order to obtain taxonomies of relationships between nodes in a network, a possibility which is also illustrated in the current article.Comment: 19 pages, 23 figure

Miniaturized optical fiber Bragg grating sensor interrogator based on echelle diffractive gratings

An Optical fiber Bragg grating sensor interrogation device based on monolithically integrated echelle diffractive grating and detector arrays on an InP chip is designed and prototyped. The device weighs less than 60 g and measures smaller than 45 mm × 30 mm × 15 mm, and it is specifically designed for potential integration into aerospace applications. This study discusses this device's operation principle and presents some initial experimental results reflecting its performance

Identification of the Changbaishan ‘Millennium’ (B-Tm) eruption deposit in the Lake Suigetsu (SG06) sedimentary archive, Japan: Synchronisation of hemispheric-wide palaeoclimate archives

The B-Tm tephra, dispersed during the highly explosive Changbaishan ‘Millennium’ eruption (ca. 940–950 CE) and a key marker layer within the Greenland ice cores, has now been identified in the Lake Suigetsu (SG06) sedimentary sequence, central Japan. The major element geochemistry of the volcanic glasses within this tephra layer are compared to a new glass dataset from the distal type-locality (Tomakomai Port, Hokkaido) and other published ‘Millennium’ eruption/B-Tm deposits, to verify this correlation. The discovery of the B-Tm tephra in the Lake Suigetsu record provides, to date, the most southerly identification of this ash and, crucially, the first direct tie-point between this high-resolution, mid-latitude palaeoclimate archive and the Greenland ice cores. These findings present significant encouragement for on-going research into the tephrostratigraphy of East Asia, focusing on the identification of widely-dispersed tephra layers which can facilitate the synchronisation of disparate palaeoclimate archives and thus enable the assessment of spatio-temporal variations in past climatic change

Theoretical approach and impact of correlations on the critical packet generation rate in traffic dynamics on complex networks

Using the formalism of the biased random walk in random uncorrelated networks with arbitrary degree distributions, we develop theoretical approach to the critical packet generation rate in traffic based on routing strategy with local information. We explain microscopic origins of the transition from the flow to the jammed phase and discuss how the node neighbourhood topology affects the transport capacity in uncorrelated and correlated networks.Comment: 6 pages, 5 figure

Antiangiogenic therapy by local intracerebral microinfusion improves treatment efficiency and survival in an orthotopic human glioblastoma model

Targeting active angiogenesis, which is a major hallmark of malignant gliomas, is a potential therapeutic approach. For effective inhibition of tumor-induced neovascularization, antiangiogenic compounds have to be delivered in sufficient quantities over a sustained period of time. The short biological half-life of many antiangiogenic inhibitors and the impaired intratumoral blood flow create logistical difficulties that make it necessary to optimize drug delivery for the treatment of malignant gliomas. In this study, we compared the effects of endostatin delivered by daily systemic administration or local intracerebral microinfusion on established intracranial U87 human glioblastoma xenografts in nude mice. Noninvasive magnetic resonance imaging methods were used to assess treatment effects and additional histopathological analysis of tumor volume, microvessel density, proliferation, and apoptosis rate were performed. Three weeks of local intracerebral microinfusion of endostatin (2 mg/kg/day) led to 74% (P < 0.05) reduction of tumor volumes with decreased microvessel densities (33.5%, P < 0.005) and a 3-fold increased tumor cell apoptosis (P < 0.002). Systemic administration of a 10-fold higher amount of endostatin (20 mg/kg/day) did not result in a reduction of tumor volume nor in an increase of tumor cell apoptosis despite a significant decrease of microvessel densities (26.9%, P < 0.005). Magnetic resonance imaging was used to successfully demonstrate treatment effects. The local microinfusion of human endostatin significantly increased survival when administered at 2 mg/kg/day and was prolonged further when the dose was increased to 12 mg/kg/day. Our results indicate that the local intracerebral microinfusion of antiangiogenic compounds is an effective way to overcome the logistical problems of inhibiting glioma-induced angiogenesis

Electronic structure of fluorides: general trends for ground and excited state properties

The electronic structure of fluorite crystals are studied by means of density functional theory within the local density approximation for the exchange correlation energy. The ground-state electronic properties, which have been calculated for the cubic structures $CaF_{2}$,$SrF_{2}$, $BaF_{2}$, $CdF_{2}$, $HgF_{2}$, $\beta$-$PbF_{2}$, using a plane waves expansion of the wave functions, show good comparison with existing experimental data and previous theoretical results. The electronic density of states at the gap region for all the compounds and their energy-band structure have been calculated and compared with the existing data in the literature. General trends for the ground-state parameters, the electronic energy-bands and transition energies for all the fluorides considered are given and discussed in details. Moreover, for the first time results for $HgF_{2}$ have been presented

Precision tests of QED and non-standard models by searching photon-photon scattering in vacuum with high power lasers

We study how to search for photon-photon scattering in vacuum at present petawatt laser facilities such as HERCULES, and test Quantum Electrodynamics and non-standard models like Born-Infeld theory or scenarios involving minicharged particles or axion-like bosons. First, we compute the phase shift that is produced when an ultra-intense laser beam crosses a low power beam, in the case of arbitrary polarisations. This result is then used in order to design a complete test of all the parameters appearing in the low energy effective photonic Lagrangian. In fact, we propose a set of experiments that can be performed at HERCULES, eventually allowing either to detect photon-photon scattering as due to new physics, or to set new limits on the relevant parameters, improving by several orders of magnitude the current constraints obtained recently by PVLAS collaboration. We also describe a multi-cross optical mechanism that can further enhance the sensitivity, enabling HERCULES to detect photon-photon scattering even at a rate as small as that predicted by QED. Finally, we discuss how these results can be improved at future exawatt facilities such as ELI, thus providing a new class of precision tests of the Standard Model and beyond.Comment: 15 pages, 2 figures. Corrected few mistakes in section and 4. Results unchanged. Added a referenc