Kinetic treatment of radiation reaction effects

Modern accelerators and light sources subject bunches of charged particles to quasiperiodic motion in extremely high electric fields, under which they may emit a substantial fraction of their energy. To properly describe the motion of these particle bunches, we require a kinetic theory of radiation reaction. We develop such a theory based on the notorious Lorentz-Dirac equation, and explore how it reduces to the usual Vlasov theory in the appropriate limit. As a simple illustration of the theory, we explore the radiative damping of Langmuir waves

Beta-cell Intrinsic Dynamics Rather than Gap Junction Structure Dictates Subpopulations in the Islet Functional Network

Diabetes is caused by the inability of electrically coupled, functionally heterogeneous -cells within the pancreatic islet to provide adequate insulin secretion. Functional networks have been used to represent synchronized oscillatory [Ca2+] dynamics and to study -cell subpopulations, which play an important role in driving islet function. The mechanism by which highly synchronized -cell subpopulations drive islet function is unclear. We used experimental and computational techniques to investigate the relationship between functional networks, structural (gap-junction) networks, and intrinsic -cell dynamics in slow and fast oscillating islets. Highly synchronized subpopulations in the functional network were differentiated by intrinsic dynamics, including metabolic activity and KATP channel conductance, more than structural coupling. Consistent with this, intrinsic dynamics were more predictive of high synchronization in the islet functional network as compared to high levels of structural coupling. Finally, dysfunction of gap junctions, which can occur in diabetes, caused decreases in the efficiency and clustering of the functional network. These results indicate that intrinsic dynamics rather than structure drive connections in the functional network and highly synchronized subpopulations, but gap junctions are still essential for overall network efficiency. These findings deepen our interpretation of functional networks and the formation of functional sub-populations in dynamic tissues such as the islet

VOBLA: a vehicle for optimized basic linear algebra

International audienceWe present VOBLA, a domain-specific language designed for programming linear algebra libraries. VOBLA is compiled to PENCIL, a domain independent intermediate language designed for efficient mapping to accelerator architectures such as GPGPUs. PENCIL is compiled to efficient, platform-specific OpenCL code using techniques based on the polyhedral model. This approach addresses both the programmer productivity and performance portability concerns associated with accelerator programming.We demonstrate our approach by using VOBLA to implement a BLAS library. We have evaluated the performance of OpenCL code generated using our compilation flow on ARM Mali, AMD Radeon, and AMD Opteron platforms. The generated code is currently on average 1.9x slower than highly hand-optimized OpenCL code, but on average 8.1x faster than straightforward OpenCL code. Given that the VOBLA coding takes significantly less effort compared to hand-optimizing OpenCL code, we believe our approach leads to improved productivity and performance portability

Тематика рефератов

© 2015 IEEE.Programming accelerators such as GPUs withlow-level APIs and languages such as OpenCL and CUDAis difficult, error-prone, and not performance-portable. Au-tomatic parallelization and domain specific languages (DSLs)have been proposed to hide complexity and regain performanceportability. We present P ENCIL, a rigorously-defined subset ofGNU C99 - enriched with additional language constructs - that enables compilers to exploit parallelism and produce highlyoptimized code when targeting accelerators. P ENCIL aims toserve both as a portable implementation language for libraries, and as a target language for DSL compilers. We implemented a P ENCIL-to-OpenCL backend using astate-of-the-art polyhedral compiler. The polyhedral compiler, extended to handle data-dependent control flow and non-affinearray accesses, generates optimized OpenCL code. To demon-strate the potential and performance portability of P ENCILand the P ENCIL-to-OpenCL compiler, we consider a numberof image processing kernels, a set of benchmarks from theRodinia and SHOC suites, and DSL embedding scenarios forlinear algebra (BLAS) and signal processing radar applications(SpearDE), and present experimental results for four GPUplatforms: AMD Radeon HD 5670 and R9 285, NVIDIAGTX 470, and ARM Mali-T604