How do programs become more concurrent? A story of program transformations

For several decades, programmers have relied onMooreâ s Law to improve the performance of their softwareapplications. From now on, programmers need to programthe multi-cores if they want to deliver efficient code. Inthe multi-core era, a major maintenance task will be tomake sequential programs more concurrent. What are themost common transformations to retrofit concurrency intosequential programs?We studied the source code of 5 open-source Javaprojects. We analyzed qualitatively and quantitatively thechange patterns that developers have used in order toretrofit concurrency. We found that these transformationsbelong to four categories: transformations that improve thelatency, the throughput, the scalability, or correctness of theapplications. In addition, we report on our experience ofparallelizing one of our own programs. Our findings caneducate software developers on how to parallelize sequentialprograms, and can provide hints for tool vendors aboutwhat transformations are worth automating

Refactoring Sequential Java Code for Concurrency via Concurrent Libraries

Parallelizing existing sequential programs to run efficiently on multicores is hard. The Java 5 packagejava.util.concurrent (j.u.c.) supports writing concurrent programs: much of the complexity of writing threads-safe and scalable programs is hidden in the library. To use this package, programmers still need to reengineer existing code. This is tedious because it requires changing many lines of code, is error-prone because programmers can use the wrong APIs, and is omission-prone because programmers can miss opportunities to use the enhanced APIs. This paper presents our tool, CONCURRENCER, which enables programmers to refactor sequential code into parallel code that uses j.u.c. concurrent utilities. CONCURRENCER does not require any program annotations, although the transformations are very involved: they span multiple program statements and use custom program analysis. A find-and-replace tool can not perform such transformations. Empirical evaluation shows that CONCURRENCER refactors code effectively: CONCURRENCER correctly identifies and applies transformations that some open-source developers overlooked, and the converted code exhibits good speedup

Towards real-time stereoscopic image rectification for 3D visualization

This paper describes a method for stereoscopic rectification with geometric distortion minimisation, to generate suitable image pairs for 3D viewing applications. The current state of the art technique is not optimal as it lacks appropriate mathematical constraints. We present a new approach that enforces the same distortion minimisation criterion with more computational e±ciency whilst also achieving superior distortion removal. Detailed mathematical expressions have been developed that fully constrain the system to facilitate the use of faster and more accurate non-linear optimisation algorithms. Appropriate rectification transforms can then be defined at speeds suitable for real-timeimplementation

Modeling of Magnetorheological Fluids by the Discrete Element Method

Magnetorheological (MR) fluids are fluids whose properties vary in response to an applied magnetic field. Such fluids are typically composed of microscopic iron particles ( 1 20 lm diameter, 20 40% by volume) suspended in a carrier fluid such as mineral oil or water. MR fluids are increasingly proposed for use in various mechanical system applications, many of which fall in the domain of tribology, such as smart dampers and clutches, prosthetic articulations, and controllable polishing fluids. The goal of this study is to present an overview of the topic to the tribology audience, and to develop an MR fluid model from the microscopic point of view using the discrete element method (DEM), with a long range objective to better optimize and understand MR fluid behavior in such tribological applications. As in most DEM studies, inter-particle forces are determined by a force-displacement law and trajectories are calculated using Newton’s second law. In this study, particle magnetization and magnetic interactions between particles have been added to the discrete element code. The global behavior of the MR fluid can be analyzed by examining the time evolution of the ensemble of particles. Microscopically, the known behavior is observed: particles align themselves with the external magnetic field. Macroscopically, averaging over a number of particles and a significant time interval, effective viscosity increases significantly when an external magnetic field is applied. These preliminary results would appear to establish that the DEM is a promising method to study MR fluids at the microscopic and macroscopic scales as an aid to tribological design. [DOI: 10.1115/1.4006021

Resolution of linear entity and path geometries expressed via partially-geospatial natural language

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 100-102).When conveying geospatial information via natural language, people typically combine implicit, commonsense knowledge with explicitly-stated information. Usually, much of this is contextual and relies on establishing locations by relating them to other locations mentioned earlier in the conversation. Because people and objects move through the world, a common and useful kind of geospatial phrase is the path expression, which is formed by designating multiple locations as landmarks on the path and relating those landmarks to one another in sequence. These phrases often include nongeospatial information, and the paths often include linear entities. This thesis builds upon the work done for the GeoCoder spatial reasoning system, by addressing several of its limitations and extending its functionality.by John Javier Marrero.M.Eng

Sample Size Sensitivity in Descriptive Baseball Statistics

[EN] This paper presents one element of a larger project that probes for systematic and predictable patterns of variability/volatility in baseball's descriptive statistics. The larger project standardizes many baseball indices along an event metric and provides relative estimates of each index’s point of inflection toward an empirical asymptote. Specifically these estimates reflect deviations in sensitivity to “sample size” (e.g., which descriptive statistics are more or less robust across events). The end purpose of this broader investigation is a qualifier to be associated with such statistics: sample size sensitivity (Triple S). Not because it's needed, but because, colloquially, discussions of baseball statistics are commonly qualified by the cautionary statement, "well, it's a small sample size". The current presentation highlights the process and results of estimating the logarithmic event function of one statistic, batting average, and we will provide real-time projections of accuracy (our estimated function versus in-coming baseball data that occurs during the CARMA conference). Results have implications for the integration of BigData applications into digestable summary statistics that appeal to a broad-reaching audience with practical implications and meaning.Kulas, J.; Wanamaker, M.; Padron-Marrero, D.; Xu, H. (2020). Sample Size Sensitivity in Descriptive Baseball Statistics. Editorial Universitat Politècnica de València. 253-258. https://doi.org/10.4995/CARMA2020.2020.11643OCS25325

Assessing the continuity of the blue ice climate record at Patriot Hills, Horseshoe Valley, West Antarctica

We use high resolution Ground Penetrating Radar (GPR) to assess the continuity of the Blue Ice Area (BIA) horizontal climate record at Patriot Hills, Horseshoe Valley, West Antarctica. The sequence contains three pronounced changes in deuterium isotopic values at ~18 cal ka, ~12 cal ka and ~8 cal ka. GPR surveys along the climate sequence reveal continuous, conformable dipping isochrones, separated by two unconformities in the isochrone layers, which correlate with the two older deuterium shifts. We interpret these incursions as discontinuities in the sequence, rather than direct measures of climate change. Ice-sheet models and Internal Layer Continuity Index plots suggest that the unconformities represent periods of erosion occurring as the former ice surface was scoured by katabatic winds in front of mountains at the head of Horseshoe Valley. This study demonstrates the importance of high resolution GPR surveys for investigating both paleo-flow dynamics and interpreting BIA climate records

Interannual surface evolution of an Antarctic blue-ice moraine using multi-temporal DEMs

Multi-temporal and fine resolution topographic data products are increasingly used to quantify surface elevation change in glacial environments. In this study, we employ 3D digital elevation model (DEM) differencing to quantify the topographic evolution of a blue-ice moraine complex in front of Patriot Hills, Heritage Range, Antarctica. Terrestrial laser scanning (TLS) was used to acquire multiple topographic datasets of the moraine surface at the beginning and end of the austral summer season in 2012/2013 and during a resurvey field campaign in 2014. A complementary topographic dataset was acquired at the end of season 1 through the application of Structure-from-Motion with multi-view stereo (SfM-MVS) photogrammetry to a set of aerial photographs acquired from an unmanned aerial vehicle (UAV).Three-dimensional cloud-to-cloud differencing was undertaken using the Multiscale Model to Model Cloud Comparison (M3C2) algorithm. DEM differencing revealed net uplift and lateral movement of the moraine crests within season 1 (mean uplift ~0.10 m), and surface lowering of a similar magnitude in some inter-moraine depressions and close to the current ice margin, although we are unable to validate the latter. Our results indicate net uplift across the site between seasons 1 and 2 (mean 0.07 m). This research demonstrates that it is possible to detect dynamic surface topographical change across glacial moraines over short (annual to intra-annual) timescales through the acquisition and differencing of fine-resolution topographic datasets. Such data offer new opportunities to understand the process linkages between surface ablation, ice flow, and debris supply within moraine ice

How do programs become more concurrent? A story of program transformations

ABSTRACT In the multi-core era, programmers need to resort to parallelism if they want to improve program performance. Thus, a major maintenance task will be to make sequential programs more concurrent. Must concurrency be designed into a program, or can it be retrofitted later? What are the most common transformations to retrofit concurrency into sequential programs? Are these transformations random, or do they belong to certain categories? How can we automate these transformations? To answer these questions we analyzed the source code of five open-source Java projects and looked at a total of 14 versions. We analyzed qualitatively and quantitatively the concurrency-related transformations. We found that these transformations belong to four categories: transformations that improve the responsiveness, the throughput, the scalability, or correctness of the applications. In 73.9% of these transformations, concurrency was retrofitted on existing program elements. In 20.5% of the transformations, concurrency was designed into new program elements. Our findings educate software developers on how to parallelize sequential programs, and provide hints for tool vendors about what transformations are worth automating