Systematic Design Methods for Efficient Off-Chip DRAM Access

Typical design flows for digital hardware take, as their input, an abstract description of computation and data transfer between logical memories. No existing commercial high-level synthesis tool demonstrates the ability to map logical memory inferred from a high level language to external memory resources. This thesis develops techniques for doing this, specifically targeting off-chip dynamic memory (DRAM) devices. These are a commodity technology in widespread use with standardised interfaces. In use, the bandwidth of an external memory interface and the latency of memory requests asserted on it may become the bottleneck limiting the performance of a hardware design. Careful consideration of this is especially important when designing with DRAMs, whose latency and bandwidth characteristics depend upon the sequence of memory requests issued by a controller. Throughout the work presented here, we pursue exact compile-time methods for designing application-specific memory systems with a focus on guaranteeing predictable performance through static analysis. This contrasts with much of the surveyed existing work, which considers general purpose memory controllers and optimized policies which improve performance in experiments run using simulation of suites of benchmark codes. The work targets loop-nests within imperative source code, extracting a mathematical representation of the loop-nest statements and their associated memory accesses, referred to as the ‘Polytope Model’. We extend this mathematical representation to represent the physical DRAM ‘row’ and ‘column’ structures accessed when performing memory transfers. From this augmented representation, we can automatically derive DRAM controllers which buffer data in on-chip memory and transfer data in an efficient order. Buffering data and exploiting ‘reuse’ of data is shown to enable up to 50× reduction in the quantity of data transferred to external memory. The reordering of memory transactions exploiting knowledge of the physical layout of the DRAM device allowing to 4× improvement in the efficiency of those data transfers

Electrically driven optical interferometry with spins in silicon carbide

Interfacing solid-state defect electron spins to other quantum systems is an ongoing challenge. The ground-state spin's weak coupling to its environment bestows excellent coherence properties, but also limits desired drive fields. The excited-state orbitals of these electrons, however, can exhibit stronger coupling to phononic and electric fields. Here, we demonstrate electrically driven coherent quantum interference in the optical transition of single, basally oriented divacancies in commercially available 4H silicon carbide. By applying microwave frequency electric fields, we coherently drive the divacancy's excited-state orbitals and induce Landau-Zener-Stuckelberg interference fringes in the resonant optical absorption spectrum. Additionally, we find remarkably coherent optical and spin subsystems enabled by the basal divacancy's symmetry. These properties establish divacancies as strong candidates for quantum communication and hybrid system applications, where simultaneous control over optical and spin degrees of freedom is paramount.Comment: 17 pages, 4 figure

The promise of whole genome pathogen sequencing for the molecular epidemiology of emerging aquaculture pathogens

Aquaculture is the fastest growing food-producing sector, and the sustainability of this industry is critical both for global food security and economic welfare. The management of infectious disease represents a key challenge. Here, we discuss the opportunities afforded by whole genome sequencing of bacterial and viral pathogens of aquaculture to mitigate disease emergence and spread. We outline, by way of comparison, how sequencing technology is transforming the molecular epidemiology of pathogens of public health importance, emphasizing the importance of community-oriented databases and analysis tools

Strong Lens Models for 37 Clusters of Galaxies from the SDSS Giant Arcs Survey

We present strong gravitational lensing models for 37 galaxy clusters from the SDSS Giant Arcs Survey. We combine data from multi-band Hubble Space Telescope WFC3imaging, with ground-based imaging and spectroscopy from Magellan, Gemini, APO, and MMT, in order to detect and spectroscopically confirm new multiply-lensed background sources behind the clusters. We report spectroscopic or photometric redshifts of sources in these fields, including cluster galaxies and background sources. Based on all available lensing evidence, we construct and present strong lensing mass models for these galaxy clusters.Comment: 53 pages; submitted to ApJ

To have and to hold: embodied ownership is established in early childhood.

We investigated whether embodied ownership is evident in early childhood. To do so, we gifted a drinking bottle to children (aged 24–48 months) to use for 2 weeks. They returned to perform reach–grasp–lift–replace actions with their own or the experimenter’s bottle while we recorded their movements using motion capture. There were differences in motor interactions with self- vs experimenter-owned bottles, such that children positioned self-owned bottles significantly closer to themselves compared with the experimenter’s bottle. Age did not modulate the positioning of the self-owned bottle relative to the experimenter-owned bottle. In contrast, the pattern was not evident in children who selected one of the two bottles to keep only after the task was completed, and thus did not ‘own’ it during the task (Experiment 2). These results extend similar findings in adults, confirming the importance of ownership in determining self–other differences and provide novel evidence that object ownership influences sensorimotor processes from as early as 2 years of age

Bayesian identification of bacterial strains from sequencing data

Rapidly assaying the diversity of a bacterial species present in a sample obtained from a hospital patient or an environmental source has become possible after recent technological advances in DNA sequencing. For several applications it is important to accurately identify the presence and estimate relative abundances of the target organisms from short sequence reads obtained from a sample. This task is particularly challenging when the set of interest includes very closely related organisms, such as different strains of pathogenic bacteria, which can vary considerably in terms of virulence, resistance and spread. Using advanced Bayesian statistical modelling and computation techniques we introduce a novel pipeline for bacterial identification that is shown to outperform the currently leading pipeline for this purpose. Our approach enables fast and accurate sequence-based identification of bacterial strains while using only modest computational resources. Hence it provides a useful tool for a wide spectrum of applications, including rapid clinical diagnostics to distinguish among closely related strains causing nosocomial infections. The software implementation is available at https://github.com/PROBIC/BIB.Peer reviewe

Lens Model and Source Reconstruction Reveal the Morphology and Star Formation Distribution in the Cool Spiral LIRG SGAS J143845.1++145407

We present $Hubble\ Space\ Telescope$ ($HST$) imaging and grism spectroscopy of a strongly lensed LIRG at $z=0.816$, SGAS 143845.1$+$145407, and use the magnification boost of gravitational lensing to study the distribution of star formation throughout this galaxy. Based on the $HST$ imaging data, we create a lens model for this system; we compute the mass distribution and magnification map of the $z=0.237$ foreground lens. We find that the magnification of the lensed galaxy ranges between $2$ and $10$, with a total magnification (measured over all the images of the source) of $\mu=11.8^{+4.6}_{-2.4}$. We find that the total projected mass density within $\sim34$ kpc of the brightest cluster galaxy is $6.0^{+0.3}_{-0.7}\times10^{12}\,M_{\odot}$. Using the lens model we create a source reconstruction for SGAS 143845.1$+$145407, which paired with a faint detection of H$\alpha$ in the grism spectroscopy, allows us to finally comment directly on the distribution of star formation in a $z\sim1$ LIRG. We find widespread star formation across this galaxy, in agreement with the current understanding of these objects. However, we note a deficit of H$\alpha$ emission in the nucleus of SGAS 143845.1$+$145407, likely due to dust extinction.Comment: 7 pages, 8 figures, 2 table