608 research outputs found
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ENZYMES: Catalysis, Kinetics and Mechanisms
Onemarvelsattheintricate designoflivingsystems,andwecannotbutwonderhow life originated on this planet. Whether ?rst biological structures emerged as the selfreproducing genetic templates (genetics-?rst origin of life) or the metabolic universality preceded the genome and eventually integrated it (metabolism-?rst origin of life) is still a matter of hot scienti?c debate. There is growing acceptance that the RNA world came ?rst тАУ as RNA molecules can perform both the functions of information storage and catalysis. Regardless of which view eventually gains acceptance, emergence of catalytic phenomena is at the core of biology. The last century has seen an explosive growth in our understanding of biological systems. The progression has involved successive emphasis on taxonomy ! physiology ! biochemistry ! molecular biology ! genetic engineering and ?nally the large-scale study of genomes. The ?eld of molecular biology became largely synonymous with the study of DNA тАУ the genetic material. Molecular biology however had its beginnings in the understanding of biomolecular structure and function. Appreciationofproteins,catalyticphenomena,andthefunctionofenzymeshadalargeroleto play in the progress of modern biology
Measuring Shadows: FPGA-based image sensor control systems for next-generation NASA missions
Astronomy and astrophysics are fields of constant growth and exploration, and discoveries are being made every day. Behind each discovery, however, is the equipment and engineering that makes that science possible. The science and engineering go hand in hand in two ways: advances in engineering make new scientific discoveries possible, and new scientific questions create the need for more advanced engineering. The work that led to this thesis is an example of the latter statement. The big-picture goal is to support the development of next-generation detectors such as the Quanta Image Sensor (QIS), a gigapixel-scaleble Complementary Metal-Oxide Semiconductor (CMOS) photon-number resolving image sensor. This thesis focuses on one crucial part of the development process: the characterisation of the QIS. In order to advance the NASA Technology Readiness Level (TRL) from three to four, the detector needs to undergo extensive laboratory and telescope environment testing. The testing framework is being run by an FPGA hardware design that includes a processor, and this set of hardware and software is responsible for operating the detector, managing experiment parameters, running experiments, and collecting resultant data and passing it to a host PC. The majority of the work of this portion of the project revolved around creating, improving, and testing the framework to allow for fully functional and automated detector characterisation. Test systems already exist for the QIS in a room temperature environment, as well as for current-generation image sensors in cryogenic vacuum environments. However, there is no existing test system that allows the QIS to be tested in a cryo-vac environment. This thesis details a functional system that fills that niche. The system is built to be modular and extensible so that it can be expanded upon to characterise other types of detectors in the future as well. For now, however, the system shines as the only one that allows the QIS to be tested in an environment that simulates its behaviour in outer space
Low-Complexity LP Decoding of Nonbinary Linear Codes
Linear Programming (LP) decoding of Low-Density Parity-Check (LDPC) codes has
attracted much attention in the research community in the past few years. LP
decoding has been derived for binary and nonbinary linear codes. However, the
most important problem with LP decoding for both binary and nonbinary linear
codes is that the complexity of standard LP solvers such as the simplex
algorithm remains prohibitively large for codes of moderate to large block
length. To address this problem, two low-complexity LP (LCLP) decoding
algorithms for binary linear codes have been proposed by Vontobel and Koetter,
henceforth called the basic LCLP decoding algorithm and the subgradient LCLP
decoding algorithm.
In this paper, we generalize these LCLP decoding algorithms to nonbinary
linear codes. The computational complexity per iteration of the proposed
nonbinary LCLP decoding algorithms scales linearly with the block length of the
code. A modified BCJR algorithm for efficient check-node calculations in the
nonbinary basic LCLP decoding algorithm is also proposed, which has complexity
linear in the check node degree.
Several simulation results are presented for nonbinary LDPC codes defined
over Z_4, GF(4), and GF(8) using quaternary phase-shift keying and
8-phase-shift keying, respectively, over the AWGN channel. It is shown that for
some group-structured LDPC codes, the error-correcting performance of the
nonbinary LCLP decoding algorithms is similar to or better than that of the
min-sum decoding algorithm.Comment: To appear in IEEE Transactions on Communications, 201
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