3,760 research outputs found
The NASA high pressure facility and turbine test rig
A description of the facility and turbine test rig is presented. Also discussed is the turbine cooling test program
HARES: an efficient method for first-principles electronic structure calculations of complex systems
We discuss our new implementation of the Real-space Electronic Structure
method for studying the atomic and electronic structure of infinite periodic as
well as finite systems, based on density functional theory. This improved
version which we call HARES (for High-performance-fortran Adaptive grid
Real-space Electronic Structure) aims at making the method widely applicable
and efficient, using high performance Fortran on parallel architectures. The
scaling of various parts of a HARES calculation is analyzed and compared to
that of plane-wave based methods. The new developments that lead to enhanced
performance, and their parallel implementation, are presented in detail. We
illustrate the application of HARES to the study of elemental crystalline
solids, molecules and complex crystalline materials, such as blue bronze and
zeolites.Comment: 17 two-column pages, including 9 figures, 5 tables. To appear in
Computer Physics Communications. Several minor revisions based on feedbac
Energy efficiency of mmWave massive MIMO precoding with low-resolution DACs
With the congestion of the sub-6 GHz spectrum, the interest in massive
multiple-input multiple-output (MIMO) systems operating on millimeter wave
spectrum grows. In order to reduce the power consumption of such massive MIMO
systems, hybrid analog/digital transceivers and application of low-resolution
digital-to-analog/analog-to-digital converters have been recently proposed. In
this work, we investigate the energy efficiency of quantized hybrid
transmitters equipped with a fully/partially-connected phase-shifting network
composed of active/passive phase-shifters and compare it to that of quantized
digital precoders. We introduce a quantized single-user MIMO system model based
on an additive quantization noise approximation considering realistic power
consumption and loss models to evaluate the spectral and energy efficiencies of
the transmit precoding methods. Simulation results show that
partially-connected hybrid precoders can be more energy-efficient compared to
digital precoders, while fully-connected hybrid precoders exhibit poor energy
efficiency in general. Also, the topology of phase-shifting components offers
an energy-spectral efficiency trade-off: active phase-shifters provide higher
data rates, while passive phase-shifters maintain better energy efficiency.Comment: Published in IEEE Journal of Selected Topics in Signal Processin
Macroservers: An Execution Model for DRAM Processor-In-Memory Arrays
The emergence of semiconductor fabrication technology allowing a tight coupling between high-density DRAM and CMOS logic on the same chip has led to the important new class of Processor-In-Memory (PIM) architectures. Newer developments provide powerful parallel processing capabilities on the chip, exploiting the facility to load wide words in single memory accesses and supporting complex address manipulations in the memory. Furthermore, large arrays of PIMs can be arranged into a massively parallel architecture. In this report, we describe an object-based programming model based on the notion of a macroserver. Macroservers encapsulate a set of variables and methods; threads, spawned by the activation of methods, operate asynchronously on the variables' state space. Data distributions provide a mechanism for mapping large data structures across the memory region of a macroserver, while work distributions allow explicit control of bindings between threads and data. Both data and work distributuions are first-class objects of the model, supporting the dynamic management of data and threads in memory. This offers the flexibility required for fully exploiting the processing power and memory bandwidth of a PIM array, in particular for irregular and adaptive applications. Thread synchronization is based on atomic methods, condition variables, and futures. A special type of lightweight macroserver allows the formulation of flexible scheduling strategies for the access to resources, using a monitor-like mechanism
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