A Performance evaluation of several ATM switching architectures

The goal of this thesis is to evaluate the performance of three Asynchronous Transfer Mode switching architectures. After examining many different ATM switching architectures in literature, the three architectures chosen for study were the Knockout switch, the Sunshine switch, and the Helical switch. A discrete-time, event driven system simulator, named ProModel, was used to model the switching behavior of these architectures. Each switching architecture was modeled and studied under at least two design configurations. The performance of the three architectures was then investigated under three different traffic types representative of traffic found in B-ISDN: random, constant bit rate, and bursty. Several key performance parameters were measured and compared between the architectures. This thesis also explored the implementation complexities and fault tolerance of the three selected architectures

Finding the growth rate of a regular language in polynomial time

We give an O(n^3+n^2 t) time algorithm to determine whether an NFA with n states and t transitions accepts a language of polynomial or exponential growth. We also show that given a DFA accepting a language of polynomial growth, we can determine the order of polynomial growth in quadratic time

The Critical Exponent is Computable for Automatic Sequences

The critical exponent of an infinite word is defined to be the supremum of the exponent of each of its factors. For k-automatic sequences, we show that this critical exponent is always either a rational number or infinite, and its value is computable. Our results also apply to variants of the critical exponent, such as the initial critical exponent of Berthe, Holton, and Zamboni and the Diophantine exponent of Adamczewski and Bugeaud. Our work generalizes or recovers previous results of Krieger and others, and is applicable to other situations; e.g., the computation of the optimal recurrence constant for a linearly recurrent k-automatic sequence.Comment: In Proceedings WORDS 2011, arXiv:1108.341

Birational maps with transcendental dynamical degree

We give examples of birational selfmaps of $\mathbb{P}^d, d \geq 3,$ whose dynamical degree is a transcendental number. This contradicts a conjecture by Bellon and Viallet. The proof uses a combination of techniques from algebraic dynamics and diophantine approximation.Comment: 49 page

Retractions

To what extent does “false science” impact the rate and direction of scientific change? We examine the impact of over 1,100 scientific retractions on the citation trajectories of articles that are related to retracted papers in intellectual space but were published prior to the retraction event. Following retraction and relative to carefully selected controls, related articles experience a lasting five to ten percent decline in the rate of citations received. This penalty is more severe when the retracted article involves fraud or misconduct, rather than honest mistakes. In addition, we find that the arrival rate of new articles and funding ows into these fields decrease after a retraction.National Science Foundation (U.S.) (SciSIP Program Award SBE-0738142)National Science Foundation (U.S.) (SciSIP Program Award SBE-0738394

Comments on "Viscosity of high crystal content melts: dependence on solid fraction"

Here we propose a simple modification of the parameterisation presented in Costa (2005) [Viscosity of high crystal content melts: dependence on solid fraction, Geophys. Res. Lett., 32, 2005] which improves all the main positive features of it, yet at the same time, does not show a plateau region as the solid fraction tends to 1, generally increases the performance of the model, and exactly recovers the classical well established relationships valid for small fractions.Comment: 6 pages, 2 figure, comments on a previous paper published on Geophys. Res. Let

Watch out for the Aunties! Young British Asians' accounts of identity and substance use

This paper considers how young people able to trace their origins from Pakistan or India (henceforth 'Asians'), discuss their use of, or abstention from, alcohol and tobacco in terms of religious and cultural tradition. The role of religion, ethnicity, gender and generation in the uptake or avoidance of alcohol and tobacco was explored in 19 qualitative group and individual interviews with 47 Asians aged 16–26 years and analysed in terms of pioneering and conservative forms of tradition. Religious proscriptions on alcohol and tobacco were reported to be formally gender blind, but concerns about reputation and future marriage chances, sanctioned by gossip, meant that women's behaviour was consistently more constrained than men's. Muslims' abstinence from alcohol was tightly linked with an Islamic identity in that drinking jeopardised one's claim to being a Muslim, whereas cigarette smoking was tolerated among young men. Sikhs' and Hindus' avoidance of tobacco was strongly sanctioned, but smoking did not strongly jeopardise a religious identity. Sikh men's abstention indicated manly strength central to a devout identity. Some experimentation was possible out of view of the older generation, especially the aunties, but the risk of gossip damaging young women's reputations was keenly felt. While damage to women's reputations was hard to undo, men's reputations tarnished by substance use, could be compensated for by their parents' honourable status. Discussion of tradition as innovation was rare and met with resistance. Tradition was largely experienced as a constraint to be circumvented

Improving the TanDEM-X Digital Elevation Model for flood modelling using flood extents from Synthetic Aperture Radar images

The topography of many floodplains in the developed world has now been surveyed with high resolution sensors such as airborne LiDAR (Light Detection and Ranging), giving accurate Digital Elevation Models (DEMs) that facilitate accurate flood inundation modelling. This is not always the case for remote rivers in developing countries. However, the accuracy of DEMs produced for modelling studies on such rivers should be enhanced in the near future by the high resolution TanDEM-X WorldDEM. In a parallel development, increasing use is now being made of flood extents derived from high resolution Synthetic Aperture Radar (SAR) images for calibrating, validating and assimilating observations into flood inundation models in order to improve these. This paper discusses an additional use of SAR flood extents, namely to improve the accuracy of the TanDEM-X DEM in the floodplain covered by the flood extents, thereby permanently improving this DEM for future flood modelling and other studies. The method is based on the fact that for larger rivers the water elevation generally changes only slowly along a reach, so that the boundary of the flood extent (the waterline) can be regarded locally as a quasi-contour. As a result, heights of adjacent pixels along a small section of waterline can be regarded as samples with a common population mean. The height of the central pixel in the section can be replaced with the average of these heights, leading to a more accurate estimate. While this will result in a reduction in the height errors along a waterline, the waterline is a linear feature in a two-dimensional space. However, improvements to the DEM heights between adjacent pairs of waterlines can also be made, because DEM heights enclosed by the higher waterline of a pair must be at least no higher than the corrected heights along the higher waterline, whereas DEM heights not enclosed by the lower waterline must in general be no lower than the corrected heights along the lower waterline. In addition, DEM heights between the higher and lower waterlines can also be assigned smaller errors because of the reduced errors on the corrected waterline heights. The method was tested on a section of the TanDEM-X Intermediate DEM (IDEM) covering an 11km reach of the Warwickshire Avon, England. Flood extents from four COSMO-SKyMed images were available at various stages of a flood in November 2012, and a LiDAR DEM was available for validation. In the area covered by the flood extents, the original IDEM heights had a mean difference from the corresponding LiDAR heights of 0.5 m with a standard deviation of 2.0 m, while the corrected heights had a mean difference of 0.3 m with standard deviation 1.2 m. These figures show that significant reductions in IDEM height bias and error can be made using the method, with the corrected error being only 60% of the original. Even if only a single SAR image obtained near the peak of the flood was used, the corrected error was only 66% of the original. The method should also be capable of improving the final TanDEM-X DEM and other DEMs, and may also be of use with data from the SWOT (Surface Water and Ocean Topography) satellite