3,939 research outputs found
ARM Wrestling with Big Data: A Study of Commodity ARM64 Server for Big Data Workloads
ARM processors have dominated the mobile device market in the last decade due
to their favorable computing to energy ratio. In this age of Cloud data centers
and Big Data analytics, the focus is increasingly on power efficient
processing, rather than just high throughput computing. ARM's first commodity
server-grade processor is the recent AMD A1100-series processor, based on a
64-bit ARM Cortex A57 architecture. In this paper, we study the performance and
energy efficiency of a server based on this ARM64 CPU, relative to a comparable
server running an AMD Opteron 3300-series x64 CPU, for Big Data workloads.
Specifically, we study these for Intel's HiBench suite of web, query and
machine learning benchmarks on Apache Hadoop v2.7 in a pseudo-distributed
setup, for data sizes up to files, web pages and tuples. Our
results show that the ARM64 server's runtime performance is comparable to the
x64 server for integer-based workloads like Sort and Hive queries, and only
lags behind for floating-point intensive benchmarks like PageRank, when they do
not exploit data parallelism adequately. We also see that the ARM64 server
takes the energy, and has an Energy Delay Product (EDP) that
is lower than the x64 server. These results hold promise for ARM64
data centers hosting Big Data workloads to reduce their operational costs,
while opening up opportunities for further analysis.Comment: Accepted for publication in the Proceedings of the 24th IEEE
International Conference on High Performance Computing, Data, and Analytics
(HiPC), 201
Truthful Facility Assignment with Resource Augmentation: An Exact Analysis of Serial Dictatorship
We study the truthful facility assignment problem, where a set of agents with
private most-preferred points on a metric space are assigned to facilities that
lie on the metric space, under capacity constraints on the facilities. The goal
is to produce such an assignment that minimizes the social cost, i.e., the
total distance between the most-preferred points of the agents and their
corresponding facilities in the assignment, under the constraint of
truthfulness, which ensures that agents do not misreport their most-preferred
points.
We propose a resource augmentation framework, where a truthful mechanism is
evaluated by its worst-case performance on an instance with enhanced facility
capacities against the optimal mechanism on the same instance with the original
capacities. We study a very well-known mechanism, Serial Dictatorship, and
provide an exact analysis of its performance. Although Serial Dictatorship is a
purely combinatorial mechanism, our analysis uses linear programming; a linear
program expresses its greedy nature as well as the structure of the input, and
finds the input instance that enforces the mechanism have its worst-case
performance. Bounding the objective of the linear program using duality
arguments allows us to compute tight bounds on the approximation ratio. Among
other results, we prove that Serial Dictatorship has approximation ratio
when the capacities are multiplied by any integer . Our
results suggest that even a limited augmentation of the resources can have
wondrous effects on the performance of the mechanism and in particular, the
approximation ratio goes to 1 as the augmentation factor becomes large. We
complement our results with bounds on the approximation ratio of Random Serial
Dictatorship, the randomized version of Serial Dictatorship, when there is no
resource augmentation
Mechanics guided design of hybrid laser/waterjet system for machining of hard and brittle materials
The two main objectives of this work is 1) to develop a mathematical model to efficiently capture the fracture behavior of materials undergoing thermal shock and 2) to design and develop a mechanics based hybrid laser/waterjet manufacturing process that will be able to machine hard and brittle materials at higher speeds and with better cut quality. The mathematical model relates the temperature generated during the machining process to the fracture behavior observed during machining. The hybrid manufacturing processes produces a synergetic effect of both laser and waterjet processes and overcomes the disadvantages of both of them.
The temperature distribution is obtained from the Green\u27s solution of the Fourier Heat Conduction equation. Uncoupled thermoelastic stresses are obtained from the temperature distribution which in-turn is related to the stress intensity factor/Griffith Energy for Mode I crack growth by Bueckner\u27s weight function approach. This model can also be used to predict fracture behavior for given laser processing conditions. This model can also be used to manipulate transformational stresses that occur during machining of high conductive materials. This model can be easily extended to many multi-physics problems involving thermo-elastic behavior
Parallel surface reconstruction through virtual milling
Surface definition deals with representing a surface analytically using a finite number of parameters and with acceptable levels of error. In the past few years it has become a key discipline in Computational Fluid Dynamics (CFD). Recent advances in computers and numerical algorithms have made it possible for CFD practitioners to attempt flow solutions about complex three-dimensional geometries. The first step in this process is having a numerical representation of the shape. In many cases of interest such a representation already exists; i.e., aircraft designed on a computer. Such Computer-Aided Design (CAD) descriptions do not exist, though, for objects found in nature or predating CAD. In such situations a technique for measuring the object and then constructing a surface conforming to these measurements is needed;Existing techniques for 3-D surface definition often require considerable human intervention, both in the measuring and the reconstruction process. This is a time consuming proposition. It is desirable to develop a fully automated alternative;Three-dimensional objects can be measured accurately and quickly from multiple viewpoints using a Cyberware laser digitizer. The digitizer returns the coordinates of a set of surface points. The problem is then to construct a faithful representation of the original object from these points. The algorithm proposed here has two distinct stages. In the first stage, surface fragments, using information from a single view, are produced by employing a visibility constraint and a 2-D Delaunay triangulation technique. In the next stage, surfaces from multiple views are combined through an approach that emulates the machining operation of milling. The final result is a non-convex, triangular faceted, polyhedron that approximates the object shape;A sequential version of the virtual milling algorithm exists on a Silicon Graphics workstation. The algorithm is of O(NlogN) complexity, where N is the number of data points. Experimental results have been obtained for a scaled F117-A model scanned from multiple viewpoints. Several topological issues have been addressed;A parallel version of the algorithm has been implemented on the Intel Gamma Prototype, a 128 node, distributed-memory, MIMD computer. Run times are compared to those obtained on an Iris 310/VGX workstation
Forests Fanned by Waves: Embodied Ways of Knowing in a Mangrove Landscape
This narrative article explores a boatman's intimate relationship with the mangrove forests he had grown up with from his childhood. The author listens to the boatman's stories about his life when he is in his sixties. How he assessed the author also implied what part of his world the author would be invited to see. This is a narrative of warmth and friendship built through traversing the mangrove forest in a handmade raft, watching birdlife, lotuses and other mangrove species. The narrative captures the ecosophy of this boatman in his lived and embodied experience
Creep, Fatigue and Creep-Fatigue Interactions in Modified 9% Cr - 1% Mo (P91) Steels
Grade P91 steel, from the class of advanced high-chrome ferritic steels, is one of the preferred materials for many elevated temperature structural components. Creep-fatigue (C-F) interactions, along with oxidation, can accelerate the kinetics of damage accumulation and consequently reduce such components\u27 life. Hence, reliable C-F test data is required for meticulous consideration of C-F interactions and oxidation, which in turn is vital for sound design practices. It is also imperative to develop analytical constitutive models that can simulate and predict material response under various long-term in-service conditions using experimental data from short-term laboratory experiments. Consequently, the major objectives of the proposed research are to characterize the creep, fatigue and C-F behavior of grade P91 steels at 625 C and develop robust constitutive models for simulating/predicting their microstructural response under different loading conditions.
This work will utilize experimental data from 16 laboratories worldwide that conducted tests (creep, fatigue and C-F) on grade P91 steel at 625°C in a round-robin (RR) program. Along with 7 creep deformation and rupture tests, 32 pure fatigue and 46 C-F tests from the RR are considered in this work. A phenomenological constitutive model formulated in this work needs just five fitting parameters to simulate/predict the monotonic, pure fatigue and C-F behavior of grade P91 at 625 C. A modified version of an existing constitutive model is also presented for particularly simulating its isothermal creep deformation and rupture behavior.
Experimental results indicate that specimen C-F lives, as measured by the 2% load drop criterion, seem to decrease with increasing strain ranges and increasing hold times at 625°C. Metallographic assessment of the tested specimens shows that the damage mode in both pure fatigue and 600 seconds hold time cyclic tests is predominantly transgranular fatigue with some presence of oxidation spikes. The damage mode in 1800 second hold time cyclic tests is an interaction of transgranular fatigue with dominant oxide spikes and creep cavitation. Other experimental results including the statistical analysis and inter- and intra-laboratory variability in the C-F lifetimes are provided in the text. Scatter factor for any of creep, monotonic, pure fatigue and C-F simulations is shown to be at a maximum of ~ 1.3, in comparison to \u3e 5 expected for a RR. Moreover, the microstructural variability between nominally homogeneous specimens can be inherently accounted by the formulated constitutive model
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