Analyzing the Performance of Lock-Free Data Structures: A Conflict-based Model

This paper considers the modeling and the analysis of the performance of lock-free concurrent data structures. Lock-free designs employ an optimistic conflict control mechanism, allowing several processes to access the shared data object at the same time. They guarantee that at least one concurrent operation finishes in a finite number of its own steps regardless of the state of the operations. Our analysis considers such lock-free data structures that can be represented as linear combinations of fixed size retry loops. Our main contribution is a new way of modeling and analyzing a general class of lock-free algorithms, achieving predictions of throughput that are close to what we observe in practice. We emphasize two kinds of conflicts that shape the performance: (i) hardware conflicts, due to concurrent calls to atomic primitives; (ii) logical conflicts, caused by simultaneous operations on the shared data structure. We show how to deal with these hardware and logical conflicts separately, and how to combine them, so as to calculate the throughput of lock-free algorithms. We propose also a common framework that enables a fair comparison between lock-free implementations by covering the whole contention domain, together with a better understanding of the performance impacting factors. This part of our analysis comes with a method for calculating a good back-off strategy to finely tune the performance of a lock-free algorithm. Our experimental results, based on a set of widely used concurrent data structures and on abstract lock-free designs, show that our analysis follows closely the actual code behavior.Comment: Short version to appear in DISC'1

Functional failure sequences in traffic accidents

This thesis examines the interactions between road users and the factors that contribute to the occurrence of traffic accidents, and discusses the implications of these interactions with regards to driver behaviour and accident prevention measures. Traffic accident data is collected on a macroscopic level by local police authorities throughout the UK. This data provides a description of accident related factors on a macroscopic level which does not allow for a complete understanding of the interaction between the various road users or the influence of errors made by active road users. Traffic accident data collected on a microscopic level analysis of real world accident data, explaining why and how an accident occurred, can further contribute to a data driven approach to provide safety measures. This data allows for a better understanding of the interaction of factors for all road users within an accident that is not possible with other data collection methods. In the first part of the thesis, a literature review presents relevant research in traffic accident analysis and accident causation research, afterwards three accident causation models used to understand behaviour and factors leading to traffic accidents are introduced. A comparison study of these accident causation coding models that classify road user error was carried out to determine a model that would be best suited to code the accident data according to the thesis aims. Latent class cluster analyses were made of two separate datasets, the UK On the Spot (OTS) in-depth accident investigation study and the STATS19 national accident database. A comparison between microscopic (in-depth) accident data and macroscopic (national) accident data was carried out. This analysis allowed for the interactions between all relevant factors for the road users involved in the accident to be grouped into specific accident segmentations based on the cluster analysis results. First, all of the cases that were collected by the OTS team between the years 2000 to 2003 were analysed. Results suggested that for single vehicle accidents males and females typically made failures related to detection and execution issues, whereas male road users made diagnosis failures with speed as a particularly important factor. In terms of the multiple vehicle accidents the interactions between the first two road users and the subsequent accident sequence were demonstrated. A cluster analysis of all two vehicle accidents in Great Britain in the year 2005 and recorded within the STATS19 accident database was carried out as a comparison to the multiple vehicle accident OTS data. This analysis demonstrated the necessity of in-depth accident causation data in interpreting accident scenarios, as the resulting accident clusters did not provide significant differences between the groups to usefully segment the crash population. Relevant human factors were not coded for these cases and the level of detail in the accident cases did not allow for a discussion of countermeasure implications. An analysis of 428 Powered Two Wheeler accidents that were collected by the OTS team between the years 2000 to 2010 was carried out. Results identified 7 specific scenarios, the main types of which identified two particular looked but did not see accidents and two types of single vehicle PTW accidents. In cases where the PTW lost control, diagnosis failures were more common, for road users other than the PTW rider, detection issues were of particular relevance. In these cases the interaction between all relevant road users was interpreted in relation to one another. The subsequent study analysed 248 Pedestrian accidents that were collected by the OTS team between the years 2000 to 2010. Results identified scenarios related to pedestrians as being in a hurry and making detection errors, impairment due to alcohol, and young children playing in the roadside. For accidents that were initiated by the other road user s behaviour pedestrians were either struck after an accident had already occurred or due to the manoeuvre that a road user was making, older pedestrians were over-represented in this accident type. This thesis concludes by discussing how (1) microscopic in-depth accident data is needed to understand accident mechanisms, (2) a data mining approach using latent class clustering can benefit the understanding of failure mechanisms, (3) accident causation analysis is necessary to understand the types of failures that road users make and (4) accident scenario development helps quantify accidents and allows for accident countermeasure implication discussion. The original contribution to knowledge is the demonstration that when relevant data is available there is a possibility to understand the interactions that are occurring between road users before the crash, that is not possible otherwise. This contribution has been demonstrated by highlighting how latent class cluster analysis combined with accident causation data allows for relevant interactions between road users to be observed. Finally implications for this work and future considerations are outlined

Reverse polarized inductive coupling to transmit and receive radiofrequency coil arrays

Cataloged from PDF version of article.In this study, the reverse polarization method is implemented using transmit and receive arrays to improve the visibility of the interventional devices. Linearly polarized signal sourcesinductively and receptively coupled radiofrequency coilsare used in the experimental setups to demonstrate the ability of the method to separate these sources from a forward polarized anatomy signal. Two different applications of the reverse polarization method are presented here: (a) catheter tracking and (b) fiducial marker visualization, in both of which transmit and receive arrays are used. The performance of the reverse polarization method was further tested with phantom and volunteer studies, and the results proved the feasibility of this method with transmit and receive arrays. Magn Reson Med, 2012. (C) 2011 Wiley Periodicals, In

MRI-guided gene therapy

Cataloged from PDF version of article.MRI has the ability to generate high-contrast and high-resolution images, to obtain multiple diagnostic evaluations of organ function and morphology, and to provide multiple image planes with no risk of ionizing radiation. Recent efforts have focused on using MR technology to monitor gene delivery, to enhance gene transfection/transduction, and to track gene expression. This review summarizes the current status of MRIguided gene therapy. (C) 2006 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societie

Simulation of higher harmonics generation in tapping-mode atomic force microscopy

Cataloged from PDF version of article.In tapping-mode atomic force microscopy, nonlinear tip–sample interactions give rise to higher harmonics of the cantilever vibration. We present an electrical circuit to model the atomic force microscope cantilever with its first three flexural eigenmodes. An electrical circuit simulator is used to simulate the tapping-mode operation. Amplitude and phase responses of the third flexural eigenmode are obtained for different sample properties. It is found that amplitude and phase of higher harmonics depend highly on sample properties. © 2001 American Institute of Physic

An Optimized Isolation Network for the Wilkinson Divider

Cataloged from PDF version of article.We propose an isolation network to simultaneously improve the input return loss, output return loss and isolation of the Wilkinson power divider in a wide bandwidth. The required even mode and odd mode reflection coefficients of the isolation network are calculated. Constructed even and odd mode circuits are combined to give the desired isolation network. Analytical expressions for the optimal component values for a single-section divider are given. Compared with the single-section Wilkinson divider, the final design can triple the bandwidth for an input-output return loss and isolation of greater than 25 dB. Broadband characteristic is achieved without increasing the number of sections hence extra length and insertion loss are avoided. Wide operation bandwidth of the new divider is verified by experimental results. The proposed method can be applied to a two-section divider, also broadening its bandwidth

Enhancing higher harmonics of a tapping cantilever by excitation at a submultiple of its resonance frequency

Cataloged from PDF version of article.In a tapping-mode atomic force microscope, the frequency spectrum of the oscillating cantilever contains higher harmonics at integer multiples of the excitation frequency. When the cantilever oscillates at its fundamental resonance frequency w(1), the high Q-factor damps the amplitudes of the higher harmonics to negligible levels, unless the higher flexural eigenmodes are coincident with those harmonics. One can enhance the nth harmonic by the Q factor when the cantilever is excited at a submultiple of its resonance frequency (w(1)/n). Hence, the magnitude of the nth harmonic can be measured easily and it can be utilized to examine the material properties. We show theoretically that the amplitude of enhanced higher harmonic increases monotonically for a range of sample stiffness, if the interaction is dominated by elastic force

Kranijalna mezenterična arterija u dikobraza (Hystrix cristata).

The aim of this study was to investigate the arteria mesenterica cranialis and its branches in the porcupine (Hystrix cristata). Nine adult porcupines (5 males, 4 females) were each injected with a coloured latex mixture from the aortic arch for demonstration of the arteria mesenterica cranialis. The results indicated that the arteria colica dextra was anastomosed with the arteria colica media and the ramus colicus. The arteria pancreaticoduodenalis caudalis separated from the arteria mesenterica cranialis as a third branch after the arteria colica media and the arteria colica dextra. Vascularization of the jejenum was made by the jejunal arteries, which originated from the arteria mesenterica cranialis and truncus jejunalis. The arteria ileocolica was continuous with the arteria mesenterica cranialis after giving off the jejunal arteries. Vascularization of the ileum was supplied by the ramus ilealis and the ramus ilei mesenterialis. The arteria ileocolica ended by separating into the rami colici and arteria cecalis. In summary, in the present study the branches of the arteria mesenterica cranialis were studied for the first time in porcupines. The results of this study may contribute to the data in this area of science.Istražena je arteria mesenterica cranialis i njezine grane u dikobraza (Hystrix cristata). Svakom od devet odraslih dikobraza (pet mužjaka i četiri ženke) injicirana je obojena mješavina lateksa kroz luk aorte u svrhu prikaza kranijalne mezenterične arterije. Rezultati su pokazali da a. colica dextra anastomozira s a. colica media i ramus colicus. A. pancreaticoduodenalis caudalis izlazi kao treća grana kranijalne mezenterične arterije nakon srednje i desne količne arterije. Jejunum je okrvljen jejunalnim arterijama, koje su ogranci kranijalne mezenterične arterije odnosno jejunalnog debla. A. ileocolica nastavljala se na kranijalnu mezenteričnu arteriju nakon što su se odvojile jejunalne arterije. Ileum okrvljuju ramus ilealis i ramus ilei mesenterialis. A. ileocolica završava s rami colici i a. caecalis. U ovom radu po prvi put je istraženo grananje kranijalne mezenterične arterije u dikobraza