153 research outputs found
Hamiltonian Approach to Lagrangian Gauge Symmetries
We reconsider the problem of finding all local symmetries of a Lagrangian.
Our approach is completely Hamiltonian without any reference to the associated
action. We present a simple algorithm for obtaining the restrictions on the
gauge parameters entering in the definition of the generator of gauge
transformations.Comment: LaTex, 8 pages, Latex error correcte
Master Equation for Lagrangian Gauge Symmetries
Using purely Hamiltonian methods we derive a simple differential equation for
the generator of the most general local symmetry transformation of a
Lagrangian. The restrictions on the gauge parameters found by earlier
approaches are easily reproduced from this equation. We also discuss the
connection with the purely Lagrangian approach. The general considerations are
applied to the Yang-Mills theory.Comment: 14 pages, Late
Recursive Construction of Generator for Lagrangian Gauge Symmetries
We obtain, for a subclass of structure functions characterizing a first class
Hamiltonian system, recursive relations from which the general form of the
local symmetry transformations can be constructed in terms of the independent
gauge parameters. We apply this to a non-trivial Hamiltonian system involving
two primary constraints, as well as two secondary constraints of the Nambu-Goto
type.Comment: 10 pages, Late
SNATCH TECHNIQUE VALIDATION USING COMPUTATIONAL METHODS: A GENETIC ALGORITHM APPROACH
An analytical model based on a 6 degrees of freedom robotic manipulator is adopted to represent an individual athlete during weightlifting, snatch technique. The performance of
an athlete is observed and the barbell trajectory of the lifter is considered as the lifting clue of our model. The inverse kinematics problem is solved using genetic algorithm. The
results could be adopted in enhancing athletic performance through provision of an alternative weightlifting technique for the individual athlete. The performance of the athlete is compared with the generated motion. It is shown that the overall torque applied to the joints can be lessened by having the trunk horizontal angle constant during the first pull. The computational support of the technique is the main focus of the paper
Occurrence and antimicrobial resistance of emergent Arcobacter spp. isolated from cattle and sheep in Iran
This study is conducted to determine the occurrence and antimicrobial resistance of Arcobacter spp. isolated from clinically healthy food animals. A total of 308 samples from cattle (200) and sheep (108) were collected from Shiraz slaughterhouse, southern Iran to investigate the presence of the important Arcobacter spp. using cultivation and Polymerase Chain Reaction (PCR) methods. Antimicrobial susceptibility of Arcobacter isolates was determined for 18 antibiotics using disk diffusion method. Among 308 samples, 27 (8.7) and 44 (14.28) were positive for the presence of Arcobacter species with cultivation and PCR procedures, respectively. The predominant species was A. butzleri in both cattle (58.33) and sheep (55). In addition, concurrent incidence of the species was observed in 25 of the positive samples. All Arcobacter isolates were resistant to rifampicin, vancomycin, ceftriaxone, trimethoprim and cephalothin. The isolates showed high susceptibility to tetracycline, oxytetracycline, erythromycin, ciprofloxacin, kanamycin, amikacin, gentamicin and enrofloxacin. No significant difference among cattle and sheep isolates in resistance pattern was observed. The results indicate that cattle and sheep are significant intestinal carriers for Arcobacter spp. Moreover, tetracycline and aminoglycosides showed great effects on Arcobacter species in antibiogram test and can be used for treatment of human Arcobacter infections. © 2015 Elsevier Ltd
Asynchronous Execution of Python Code on Task Based Runtime Systems
Despite advancements in the areas of parallel and distributed computing, the
complexity of programming on High Performance Computing (HPC) resources has
deterred many domain experts, especially in the areas of machine learning and
artificial intelligence (AI), from utilizing performance benefits of such
systems. Researchers and scientists favor high-productivity languages to avoid
the inconvenience of programming in low-level languages and costs of acquiring
the necessary skills required for programming at this level. In recent years,
Python, with the support of linear algebra libraries like NumPy, has gained
popularity despite facing limitations which prevent this code from distributed
runs. Here we present a solution which maintains both high level programming
abstractions as well as parallel and distributed efficiency. Phylanx, is an
asynchronous array processing toolkit which transforms Python and NumPy
operations into code which can be executed in parallel on HPC resources by
mapping Python and NumPy functions and variables into a dependency tree
executed by HPX, a general purpose, parallel, task-based runtime system written
in C++. Phylanx additionally provides introspection and visualization
capabilities for debugging and performance analysis. We have tested the
foundations of our approach by comparing our implementation of widely used
machine learning algorithms to accepted NumPy standards
An Introduction to hpxMP: A Modern OpenMP Implementation Leveraging HPX, An Asynchronous Many-Task System
Asynchronous Many-task (AMT) runtime systems have gained increasing
acceptance in the HPC community due to the performance improvements offered by
fine-grained tasking runtime systems. At the same time, C++ standardization
efforts are focused on creating higher-level interfaces able to replace OpenMP
or OpenACC in modern C++ codes. These higher level functions have been adopted
in standards conforming runtime systems such as HPX, giving users the ability
to simply utilize fork-join parallelism in their own codes. Despite innovations
in runtime systems and standardization efforts users face enormous challenges
porting legacy applications. Not only must users port their own codes, but
often users rely on highly optimized libraries such as BLAS and LAPACK which
use OpenMP for parallization. Current efforts to create smooth migration paths
have struggled with these challenges, especially as the threading systems of
AMT libraries often compete with the treading system of OpenMP.
To overcome these issues, our team has developed hpxMP, an implementation of
the OpenMP standard, which utilizes the underlying AMT system to schedule and
manage tasks. This approach leverages the C++ interfaces exposed by HPX and
allows users to execute their applications on an AMT system without changing
their code.
In this work, we compare hpxMP with Clang's OpenMP library with four linear
algebra benchmarks of the Blaze C++ library. While hpxMP is often not able to
reach the same performance, we demonstrate viability for providing a smooth
migration for applications but have to be extended to benefit from a more
general task based programming model
Design and analysis of porous functionally graded femoral prostheses with improved stress shielding
One of the most important problems of total hip replacement is aseptic loosening of the femoral component, which is related to the changes of the stress distribution pattern after implantation of the prosthesis. Stress shielding of the femur is recognized as a primary factor in aseptic loosening of hip replacements. Utilizing different materials is one of the ordinary solutions for that problem, but using functionally graded materials (FGMs) could be better than the conventional solutions. This research work aims at investigating different porous FGM implants and a real femoral bone by a 3D finite element method. The results show that a neutral functionally graded prosthesis cannot extraordinarily make changes in the stress pattern of bone and prosthesis, but an increasing functionally graded prosthesis leads a lower level of stress in the prosthesis, and a decreasing functionally graded prosthesis can properly reduce the stress shielding among these three architectures. Due to the absence of similar results in the specialized literature, this paper is likely to fill a gap in the state-of-the-art bio-implants, and provide pertinent results that are instrumental in the design of porous femoral prostheses under normal walking loading conditions
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