81 research outputs found
Визначення суттєвості впливу модифікування в складі комбінованої технології віброобробки на механічні властивості сплаву АК7
No full textThe object of research is AK7 alloy, which is subjected to the complex action of vibration and modification in the process of producing cylindrical billets by means of casting in a metal mold. One of the most problematic places is the determination of rational modes of influence of technological factors on the alloy, ensuring the satisfaction of a given level of properties in terms of their competitive nature.During the study, the methods of regression analysis were used and identified as promising methods of analysis of variance to improve the accuracy of the findings. In particular, the results of the regression analysis of experimental and industrial research data on the vibration treatment technology with a frequency of 100–150 Hz with an additional input of the ultradisperse modifier into the melt are presented. The results are obtained concerning the confirmation of the hypothesis about the significance of the influence of the modifier on the increase of the mechanical properties of the alloy: НВ, σ0.2, σs, δs, ψ. This is important because attempts to improve the properties of the alloy using the combined technological solutions invariably cause the expenditure of energy and material resources. This ensures the possibility of energy and resource savings in the process. The obtained results show that the use of modification as an additional component of the technological process increases only ψ, but reduces HB and δs. In the vibration frequency range of 100–140 Hz, modification has a positive effect on σ0.2, and an increase in the frequency above this value leads to a deterioration in the result. The opposite effect is observed with respect to δs – with an increase in the vibration frequency of more than 140 Hz, modifying increases this alloy characteristic, in the range of 100–140 Hz, the introduction of a modifier can be considered justified. Thus, it is found that the modification has an ambiguous effect on the properties of the alloy, therefore, in order to select a rational technological regime, a solution to the compromise problem is necessary. This is due to the revealed fact of competing properties. It is proposed to use the methods of analysis of variance to refine the obtained results.Объектом исследования является сплав АК7, который подвергается комплексному действию вибрации и модифицирования в процессе производства цилиндрических заготовок способом литья в кокиль. Одним из самых проблемных мест является определение рациональных режимов воздействия технологических факторов на сплав, обеспечивающих удовлетворение заданного уровня свойств в условиях их конкурирующей природы.В ходе исследования использовались методы регрессионного анализа и определялись как перспективные методы дисперсионного анализа для повышения точности выводов. В частности, приведены результаты регрессионного анализа данных экспериментально-промышленных исследований технологии виброобработки с частотой 100–150 Гц с дополнительным вводом в расплав ультрадисперсного модификатора. Получены результаты, касающиеся подтверждения гипотезы о значимости влияния модификатора на повышение механических свойств сплава: НВ, σ0.2, σs, δs, ψ. Это важно, потому что попытки повысить свойства сплава использованием комбинированных технологических решений неизменно вызывает затраты энергии и материальных ресурсов. Благодаря этому обеспечивается возможность энерго- и ресурсосбережений в технологическом процессе. Полученные результаты показали, что использование модифицирования как дополнительной составляющей технологического процесса повышает только ψ, но уменьшает НВ и σs. В диапазоне частоты вибрации 100–140 Гц модифицирование положительно влияет на σ0.2, повышение же частоты выше этой величины приводит к ухудшению результата. Обратный эффект наблюдается относительно δs – с повышением частоты вибрации более 140 Гц модифицирование повышает эту характиристику сплава, в диапазоне 100–140 Гц введение модификатора можно считать обоснованным. Таким образом, установлено, что модифицирование неоднозначно влияет на свойства сплава, поэтому для выбора рационального технологического режима нужно решение компромиссной задачи. Это связано с выявленным фактом конкурирующих свойств. Предложено для уточнения полученных результатов использовать методы дисперсионного анализа.Об'єктом дослідження є сплав АК7, що піддається комплексній дії вібрації та модифікування в процесі виробництва циліндричних заготовок способом лиття в кокіль. Одним з найбільш проблемних місць є визначення раціональних режимів впливу технологічних факторів на сплав, що забезпечують задоволення заданого рівня властивостей за умов їх конкуруючої природи.В ході дослідження використовувалися методи регресійного аналізу та визначалися за перспективні методи дисперсійного аналізу для підвищення точності висновків. Зокрема, наведено результати регресійного аналізу даних експериментально-промислових досліджень технології віброобробки з частотою 100–150 Гц з додатковим вводом у розплав ультрадисперсного модифікатору. Отримано результати, що стосуються підтвердження гіпотези щодо значущості впливу модифікатора на підвищення механічних властивостей сплаву: НВ, σ0.2, σs, δs, ψ. Це важливо, бо намагання підвищити властивості сплаву використанням комбінованих технологічних рішень незмінно викликає витрати енергії та матеріальних ресурсів. Завдяки цьому забезпечується можливість енерго- та ресурсозаощаджень в технологічному процесі. Отримані результати показали, що використання модифікування як додаткової складової технологічного процесу підвищую лише ψ, але зменшує НВ та σs. В діапазоні частоти вібрації 100–140 Гц модифікування позитивно впливає на σ0.2, підвищення ж частоти вище цієї величини призводить до погіршення результату. Зворотній ефект спостерігається відносно δs – з підвищенням частоти вібрації понад 140 Гц модифікування підвищує цю характиристику сплаву, в діапазоні 100–140 Гц введення модифікатора можна вважати не обгрунтованим. Таким чином, встановлено, що модифікування неоднозначно впливає на властивості сплаву, тому для вибора раціонального технологічного режиму потрібне вирішення компромісної задачі. Це пов'язано з виявленим фактом конкуруючих властивостей. Запропоновано для уточнення отриманих результатів використати методи дисперсійного аналізу
Extensible adaptation via constraint solving
No full textThis work presents the design, implementation, and evaluation of a simple programming language for expressing scheduling policies for transmission of multiple objects across a shared network connection. A key design component of the language is the ability to express constraints among the objects to be transmitted. Policies can: make ordering constraints, such as "all text objects are transmitted before any image objects"; express rules on the relative bandwidth allocations across objects of different types; reserve a certain amount of bandwidth or restrict transmission of a subset of objects. Because it is possible to express contradictory constraints, the system finds suitable approximate solutions when no precise solution is available
Extensible adaptation via constraint solving
No full textThis work presents the design, implementation, and evaluation of a simple programming language for expressing scheduling policies for transmission of multiple objects across a shared network connection. A key design component of the language is the ability to express constraints among the objects to be transmitted. Policies can: make ordering con-straints, such as “all text objects are transmitted before any image objects”; express rules on the relative bandwidth allocations across objects of different types; reserve a certain amount of bandwidth or restrict transmission of a subset of objects. Because it is possible to express contradictory constraints, the system finds suitable approximate solutions when no precise solution is available. Acknowledgments I would like to thank my advisors, Dr. Dan S. Wallach and Dr. Willy Zwaenepoel, and Dr. David B. Johnson for fruitful discussions and helpful advice. I’m grateful to Eyal de Lara for providing help with the Puppeteer system. Content
Expressiveness, programmability and portable high performance of global address space languages
No full textThe Message Passing Interface (MPI) is the library-based programming model employed by most scalable parallel applications today; however, it is not easy to use. To simplify program development, Partitioned Global Address Space (PGAS) languages have emerged as promising alternatives to MPI. Co-array Fortran (CAF), Titanium, and Unified Parallel C are explicitly parallel single-program multiple-data languages that provide the abstraction of a global shared memory and enable programmers to use one-sided communication to access remote data. This thesis focuses on evaluating PGAS languages and explores new language features to simplify the development of high performance programs in CAF. To simplify program development, we explore extending CAF with abstractions for group, Cartesian, and graph communication topologies that we call co-spaces. The combination of co-spaces, textual barriers, and single values enables effective analysis and optimization of CAF programs. We present an algorithm for synchronization strength reduction (SSR), which replaces textual barriers with faster point-to-point synchronization. This optimization is both difficult and error-prone for developers to perform manually. SSR-optimized versions of Jacobi iteration and the NAS MG and CG benchmarks yield performance similar to that of our best hand-optimized variants and demonstrate significant improvement over their barrier-based counterparts. To simplify the development of codes that rely on producer-consumer communication, we explore extending CAF with multi-version variables (MVVs). MVVs increase programmer productivity by insulating application developers from the details of buffer management, communication, and synchronization. Sweep3D, NAS BT, and NAS SP codes expressed using MVVs are much simpler than the fastest hand-coded variants, and experiments show that they yield similar performance. To avoid exposing latency in distributed memory systems, we explore extending CAF with distributed multithreading (DMT) based on the concept of function shipping. Function shipping facilitates co-locating computation with data as well as executing several asynchronous activities in the remote and local memory. DMT uses co-subroutines/cofunctions to ship computation with either blocking or non-blocking semantics. A prototype implementation and experiments show that DMT simplifies development of parallel search algorithms and the performance of DMT-based RandomAccess exceeds that of the reference MPI implementation
Extensible Adaptation via Constraint Solving
No full textThis work presents the design, implementation, and evaluation of a simple programming language for expressing scheduling policies for transmission of multiple objects across a shared network connection. A key design component of the language is the ability to express constraints among the objects to be transmitted. Policies can: make ordering constraints, such as "all text objects are transmitted before any image objects''; express rules on the relative bandwidth allocations across objects of different types; reserve a certain amount of bandwidth or restrict transmission of a subset of objects. Because it is possible to express contradictory constraints, the system finds suitable approximate solutions when no precise solution is available
Expressiveness, Programmability and Portable High Performance of Global Address Space Languages
No full textThe Message Passing Interface (MPI) is the library-based programming model employed by most scalable parallel applications today; however, it is not easy to use. To simplify program development, Partitioned Global Address Space (PGAS) languages have emerged as promising alternatives to MPI. Co-array Fortran (CAF), Titanium, and Unified Parallel C are explicitly parallel single-program multiple-data languages that provide the abstraction of a global shared memory and enable programmers to use one-sided communication to access remote data. This thesis focuses on evaluating PGAS languages and explores new language features to simplify the development of high performance programs in CAF. To simplify program development, we explore extending CAF with abstractions for group, Cartesian, and graph communication topologies that we call co-spaces. The combination of co-spaces, textual barriers, and single values enables effective analysis and optimization of CAF programs. We present an algorithm for synchronization strength reduction (SSR), which replaces textual barriers with faster point-to-point synchronization. This optimization is both difficult and error-prone for developers to perform manually. SSR-optimized versions of Jacobi iteration and the NAS MG and CG benchmarks yield performance similar to that of our best hand-optimized variants and demonstrate significant improvement over their barrier-based counterparts. To simplify the development of codes that rely on producer-consumer communication, we explore extending CAF with multi-version variables (MVVs). MVVs increase programmer productivity by insulating application developers from the details of buffer management, communication, and synchronization. Sweep3D, NAS BT, and NAS SP codes expressed using MVVs are much simpler than the fastest hand-coded variants, and experiments show that they yield similar performance. To avoid exposing latency in distributed memory systems, we explore extending CAF with distributed multithreading (DMT) based on the concept of function shipping. Function shipping facilitates co-locating computation with data as well as executing several asynchronous activities in the remote and local memory. DMT uses co-subroutines/cofunctions to ship computation with either blocking or non-blocking semantics. A prototype implementation and experiments show that DMT simplifies development of parallel search algorithms and the performance of DMT-based Random Access exceeds that of the reference MPI implementation
*Corresponding author
No full textAbstract: Accurate reconstruction of phylogenetic trees often involves solving hard optimisation problems, particularly the Maximum Parsimony (MP) and Maximum Likelihood (ML) problems. Various heuristics yield good results for these problems within reasonable time only on small datasets. This is a major impediment for large-scale phylogeny reconstruction. Roshan et al. introduced Rec-I-DCM3, an efficient and accurate meta-method for solving the MP problem on large datasets of up to 14,000 taxa. We improve the performance of Rec-I-DCM3 via parallelisation. The experiments demonstrate that our parallel method, PRec-I-DCM3, achieves significant improvements, both in speed and accuracy, over its sequential counterpart
Correlation function of four spins in the percolation model
No full textAbstractBy using the Coulomb gas technics we calculate the four-spin correlation function in the percolation q→1 limit of the Potts model.It is known that the four-point functions define the actual fusion rules of a particular model. In this respect, we find that fusion of two spins, of dimension Δσ=596, produce a new channel, in the 4-point function, which is due to the operator with dimension Δ=5/8
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