Monitoring of aerosol particle concentrations (PM 10 , PM 2.5 , PM 1 ) and chemical analysis (PM 10 ) was undertaken at a major European airport (El Prat, Barcelona) for a whole month during autumn 2007. Concentrations of airborne PM at the airport were close to those at road traffic hotspots in the nearby Barcelona city, with means measuring 48 mg PM 10 /m 3 , 21 mg PM 2.5 /m 3 and 17 mg PM 1 /m 3 . Meteorological controls on PM at El Prat are identified as cleansing daytime sea breezes with abundant coarse salt particles, alternating with nocturnal land-sourced winds which channel air polluted by industry and traffic (PM 1 /PM 10 ratios > 0.5) SE down the Llobregat Valley. Chemical analyses of the PM 10 samples show that crustal PM is dominant (38% of PM 10 ), followed by total carbon (OC + EC, 25%), secondary inorganic aerosols (SIA, 20%), and sea salt (6%). Local construction work for a new airport terminal was an important contributor to PM 10 crustal levels. Source apportionment modelling PCA-MLRA identifies five factors: industrial/traffic, crustal, sea salt, SIA, and K + likely derived from agricultural biomass burning. Whereas most of the atmospheric contamination concerning ambient air PM 10 levels at El Prat is not attributable directly to aircraft movement, levels of carbon are unusually high (especially organic carbon), as are metals possibly sourced from tyre detritus/smoke in runway dust (Ba, Zn, Mo) and from brake dust in ambient PM 10 (Cu, Sb), especially when the airport is at its most busy. We identify microflakes of aluminous alloys in ambient PM 10 filters derived from corroded fuselage and wings as an unequivocal and highly distinctive tracer for aircraft movement.
Barrier is a very common synchronization method used in parallel programming. Barriers are used typically to enforce a partial thread execution order, since there may be dependences between code sections before and after the barrier. This work proposes TMbarrier, a new design of a barrier intended to be used in transactional applications. TMbarrier allows threads to continue executing speculatively after the barrier assuming that there are not dependences with safe threads that have not yet reached the barrier. Our design leverages transactional memory (TM) (specifically, the implementation offered by the IBM POWER8 processor) to hold the speculative updates and to detect possible conflicts between speculative and safe threads. Despite the limitations of the best-effort hardware TM implementation present in current processors, experiments show a reduction in wasted time due to synchronization compared to standard barriers.
As a recently consolidated paradigm for optimistic concurrency in modern multicore architectures, Transactional Memory (TM) can help to the exploitation of parallelism in irregular applications when data dependence information is not available up to runtime. This paper presents and discusses how to leverage TM to exploit parallelism in an important class of irregular applications, the class that exhibits irregular reduction patterns. In order to test and compare our techniques with other solutions, they were implemented in a software TM system called ReduxSTM, that acts as a proof of concept. Basically, ReduxSTM combines two major ideas: a sequential-equivalent ordering of transaction commits that assures the correct result, and an extension of the underlying TM privatization mechanism to reduce unnecessary overhead due to reduction memory updates as well as unnecesary aborts and rollbacks. A comparative study of STM solutions, including ReduxSTM, and other more classical approaches to the parallelization of reduction operations is presented in terms of time, memory and overhead.
The exploitation of optimistic concurrency in modern multicore architectures via Transactional Memory (TM) is becoming a mainstream programming paradigm. TM features can be leveraged to provide support for speculative parallel execution of irregular applications, characterized by a lack of knowledge about data dependences at compile-time. This work is focused on software TM (STM) solutions and how they can be adapted and optimized to deal efficiently with irregular memory access patterns, mainly those caused by reduction operations. With this aim, ReduxSTM is introduced as a specific STM system designed by combining techniques for speculative execution with TM algorithms. ReduxSTM is based on three main design aspects: a transactional commit order mechanism which is available to guarantee sequential semantics when needed; a specific transactional memory primitive defined for expressing commutative and associative operations (reductions) that leverages the underlying TM privatization mechanism to avoid unnecessary transaction aborts caused by reduction memory patterns; and an enhanced conflict resolution mechanism that takes advantage of the two previous features.
Transactional memory (TM) offers optimistic concurrency support in modern multicore architectures, helping the programmers to extract parallelism when data dependence information is not statically available. This work presents ReduxSTM, a software TM system especially designed to extract parallelism from irregular applications. Commit management and conflict detection are tailored to take advantage of both, sequential transaction ordering to assure correct results, and privatization of reduction patterns, a very frequent memory access pattern in irregular applications. Both techniques are used to avoid unnecessary transaction aborts.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.