Improved Acceleration of the GPU Fourier Domain Acceleration Search Algorithm

We present an improvement of our implementation of the Correlation Technique for the Fourier Domain Acceleration Search (FDAS) algorithm on Graphics Processor Units (GPUs) (Dimoudi & Armour 2015; Dimoudi et al. 2017). Our new improved convolution code which uses our custom GPU FFT code is between 2.5 and 3.9 times faster the than our cuFFT-based implementation (on an NVIDIA P100) and allows for a wider range of filter sizes then our previous version. By using this new version of our convolution code in FDAS we have achieved 44% performance increase over our previous best implementation. It is also approximately 8 times faster than the existing PRESTO GPU implementation of FDAS (Luo 2013). This work is part of the AstroAccelerate project (Armour et al. 2002), a many-core accelerated time-domain signal processing library for radio astronomy.Comment: proceeding from ADASS XXVII conference, 4 page

Computational Methods and Graphical Processing Units for Real-time Control of Tomographic Adaptive Optics on Extremely Large Telescopes.

Ground based optical telescopes suffer from limited imaging resolution as a result of the effects of atmospheric turbulence on the incoming light. Adaptive optics technology has so far been very successful in correcting these effects, providing nearly diffraction limited images. Extremely Large Telescopes will require more complex Adaptive Optics configurations that introduce the need for new mathematical models and optimal solvers. In addition, the amount of data to be processed in real time is also greatly increased, making the use of conventional computational methods and hardware inefficient, which motivates the study of advanced computational algorithms, and implementations on parallel processors. Graphical Processing Units (GPUs) are massively parallel processors that have so far demonstrated a very high increase in speed compared to CPUs and other devices, and they have a high potential to meet the real-time restrictions of adaptive optics systems. This thesis focuses on the study and evaluation of existing proposed computational algorithms with respect to computational performance, and their implementation on GPUs. Two basic methods, one direct and one iterative are implemented and tested and the results presented provide an evaluation of the basic concept upon which other algorithms are based, and demonstrate the benefits of using GPUs for adaptive optics

The influence of bioclimatic urban redevelopment on outdoor thermal comfort.

One of the greatest environmental challenges for the sustainability of future cities is the mitigation of the urban heat island phenomenon and thus, improvement of outdoor comfort conditions for people. The emphasis of this work is to analyze how mitigation techniques in a dense urban environment affect microclimate parameters and outdoor thermal comfort. The quantitative differentiation of outdoor thermal comfort conditions through bioclimatic urban redevelopment for an area in the city of Serres, Greece is investigated. The main bioclimatic interventions concern the application of cool paving materials, the increase of vegetated areas and the creation of water surfaces. The analysis and comparison are performed for a hot summer day with the ENVI-met model. Software simulations regarding microclimatic and outdoor thermal comfort conditions are performed for the daytime period 06.00–20.00 (14 h) at the height of 1.8 m from the ground. The examined parameters are air temperature, surface temperature and mean radiant temperature (Tmrt). The evaluation of outdoor thermal comfort conditions is conducted using the index PMV (Predicted Mean Vote), adapted for outdoor conditions. The results of simulations are discussed regarding the assessment of bioclimatic interventions.N/

Micro- climate adaptation of whole building energy simulation in large complexes.

The purpose of this study was to evaluate the cooling demand during a summer day over a large city area before and after bioclimatic interventions in outdoor spaces by using whole building thermal simulation. This kind of interventions ultimately leads to a microclimatic change in a city. Prediction of microclimate data for a whole day in a large area due to changes in outdoor spaces is time and cost demanding. A model for prediction of hourly microclimatic data in a region for a whole day by employing Fourier analysis of past (measured) and future (simulated from a CFD analysis) microclimate data of a limited period (sunlight hours) was also developed. The whole building energy simulation software TAS-EDSL was applied for a quite large built space (∼500 m × 500 m), for simultaneous simulations in all buildings in the area, and took into account detailed building construction data, mutual shading between buildings and local climatic conditions. In this context, strategies and practices that a building complex should follow in the future in relation to climate change could be investigated. Simulation estimations of cooling loads of building spaces were related to buildings’ age, orientation and height. Main outcome of the study was the ability to assess building energy performance due to exterior micro- climate improvement, simultaneously, for about 200 buildings.N/

Transformation of a university building into a zero energy building in Mediterranean climate.

In the context of environmental policy, the EU has launched a series of initiatives aimed at increasing the use of energy efficiency, as it has pledged to reduce energy consumption by 20%, compared with projected levels of growth of CO2 emissions into the atmosphere by 2020. In Greece CO2 emission levels in the atmosphere have risen significantly over the past two decades [1]. For the year 2011, CO2 emissions per person in Greece correspond to 7.56 t. According to the data, this increase in emissions is reflected to a 151.2% above from the levels of 1980 and a 756% increase from 1960 levels. The building sector consumes the largest amount of energy in Greece, therefore constitutes the most important source of CO2 emissions. The energy upgrade of the building sector produces multiple benefits such as reduced energy consumption, which is consistent with the reduction of air pollution. Additionally, there is a significant improvement at the interior comfort conditions of the building, which promotes productivity and occupant health. Moreover, because of the large number of educational buildings in the country, the energy consumption of them present a significant amount of the country's total energy consumption and simultaneously has the effect of increasing the costs paid by the state budget for the operation and maintenance of public buildings. The investigation of alternative methods to reduce energy consumption in educational buildings is an important approach for sustainability and economic development of the country over time. The purpose of this paper is to study and evaluate the energy saving methods of a university building in Mediterranean climate with significant energy consumption. Additionally, through Building Information Modeling (BIM) and Computational Fluid Dynamics (CFD) software, studies considering the contribution of passive heating and cooling techniques were conducted, in order to minimize energy consumption in pursuit of desirable interior thermal comfort conditions.N/

GPU Fast Convolution via the Overlap-and-Save Method in Shared Memory

We present an implementation of the overlap-and-save method, a method for the convolution of very long signals with short response functions, which is tailored to GPUs. We have implemented several FFT algorithms (using the CUDA programming language), which exploit GPU shared memory, allowing for GPU accelerated convolution. We compare our implementation with an implementation of the overlap-and-save algorithm utilizing the NVIDIA FFT library (cuFFT). We demonstrate that by using a shared-memory-based FFT, we can achieved significant speed-ups for certain problem sizes and lower the memory requirements of the overlap-and-save method on GPUs

Αναπαραστάσεις του δημοψηφίσματος του 2015 στον ελληνόφωνο και αγγλόφωνο Τύπο

Η εργασία αυτή έχει ως στόχο τη μελέτη του τρόπου αναπαράστασης του ελληνικού δημοψηφίσματος του 2015 μέσω της εξέτασης κειμένων δημοσιογραφικού λόγου, πρωτότυπου και μεταφρασμένου. Για την υλοποίηση αυτού του στόχου ακολουθείται η μεθοδολογία της κριτικής ανάλυσης λόγου, και ειδικότερα της συστημικής λειτουργικής γραμματικής, σε σώματα κειμένων. Στο πρώτο μέρος αναλύεται η συγκρότηση συγκρίσιμου σώματος κειμένων στην ελληνική και στην αγγλική γλώσσα από δημοσιογραφικά κείμενα ελληνικών και βρετανικών εφημερίδων. Μέσω της διεξοδικής εξέτασης επιλεγμένων στοιχείων από το σώμα κειμένων, αναδεικνύεται η ιδεολογία που ρητά ή υπόρρητα αναπαράγεται από τα εξεταζόμενα κείμενα ως προς τα σημαντικότερα γεγονότα και τους δρώντες που λαμβάνουν μέρος σε αυτά. Το δεύτερο μέρος στρέφεται στο πεδίο της μετάφρασης. Συγκεκριμένα, εξετάζεται ο τρόπος αναπαράστασης των γεγονότων του δημοψηφίσματος σε μεταφρασμένα δημοσιογραφικά κείμενα. Μέσω της αντιπαραβολής των αποτελεσμάτων των δύο ερευνητικών μερών εξετάζεται κατά πόσο οι ιδεολογικές θέσεις που προβάλλουν τα μεταφράσματα συνάδουν με αυτές των πρωτότυπων κειμένων. Αναδεικνύεται με αυτόν τον τρόπο ο ρόλος του ιδεολογικού πλαισίου εντός του οποίου παράγονται τα μεταφράσματα ως προς τη διαμόρφωση των επιμέρους μεταφραστικών επιλογών και της ευρύτερης ιδεολογικής τοποθέτησης που αποτυπώνεται στο καθένα.The present thesis aims at examining the way that the 2015 Greek bailout referendum is represented in original and translated texts of journalistic discourse. The selected texts are analysed according to the principles and methods of corpus linguistics and critical discourse analysis, and in particular by following a systemic functional linguistics perspective. The first part of the thesis includes the creation of a comparable corpus of Greek and English news texts drawn from Greek and British newspapers. The detailed examination of selected corpus data reveals the explicit and implicit ideology of the texts as regards the most important events and actors that take place in them. The research part is related to the field of translation. More specifically, this part investigates the way that the events of the Greek referendum are represented in translated journalistic texts. By comparing the results between the two parts, we examined the extent to which the ideological positions of translated texts are in line with those of the originals. This analysis highlights the effect of the ideological context in which the translations are produced, on the different translation choices and the general ideology that each translation reflects

Bits missing: finding exotic pulsars using bfloat16 on NVIDIA GPUs

The Fourier domain acceleration search (FDAS) is an effective technique for detecting faint binary pulsars in large radio astronomy data sets. This paper quantifies the sensitivity impact of reducing numerical precision in the graphics processing unit (GPU)-accelerated FDAS pipeline of the AstroAccelerate (AA) software package. The prior implementation used IEEE-754 single-precision in the entire binary pulsar detection pipeline, spending a large fraction of the runtime computing GPU-accelerated fast Fourier transforms. AA has been modified to use bfloat16 (and IEEE-754 double-precision to provide a “gold standard” comparison) within the Fourier domain convolution section of the FDAS routine. Approximately 20,000 synthetic pulsar filterbank files representing binary pulsars were generated using SIGPROC with a range of physical parameters. They have been processed using bfloat16, single-precision, and double-precision convolutions. All bfloat16 peaks are within 3% of the predicted signal-to-noise ratio of their corresponding single-precision peaks. Of 14,971 “bright” single-precision fundamental peaks above a power of 44.982 (our experimentally measured highest noise value), 14,602 (97.53%) have a peak in the same acceleration and frequency bin in the bfloat16 output plane, while in the remaining 369 the nearest peak is located in the adjacent acceleration bin. There is no bin drift measured between the single- and double-precision results. The bfloat16 version of FDAS achieves a speedup of approximately 1.6× compared to single-precision. A comparison between AA and the PRESTO software package is presented using observations collected with the GMRT of PSR J1544+4937, a 2.16 ms black widow pulsar in a 2.8 hr compact orbit

A GPU implementation of the Correlation Technique for Real-time Fourier Domain Pulsar Acceleration Searches

The study of binary pulsars enables tests of general relativity. Orbital motion in binary systems causes the apparent pulsar spin frequency to drift, reducing the sensitivity of periodicity searches. Acceleration searches are methods that account for the effect of orbital acceleration. Existing methods are currently computationally expensive, and the vast amount of data that will be produced by next generation instruments such as the Square Kilometre Array (SKA) necessitates real-time acceleration searches, which in turn requires the use of High Performance Computing (HPC) platforms. We present our implementation of the Correlation Technique for the Fourier Domain Acceleration Search (FDAS) algorithm on Graphics Processor Units (GPUs). The correlation technique is applied as a convolution with multiple Finite Impulse Response filters in the Fourier domain. Two approaches are compared: the first uses the NVIDIA cuFFT library for applying Fast Fourier Transforms (FFTs) on the GPU, and the second contains a custom FFT implementation in GPU shared memory. We find that the FFT shared memory implementation performs between 1.5 and 3.2 times faster than our cuFFT-based application for smaller but sufficient filter sizes. It is also 4 to 6 times faster than the existing GPU and OpenMP implementations of FDAS. This work is part of the AstroAccelerate project, a many-core accelerated time-domain signal processing library for radio astronomy.Comment: 20 pages, 9 figures. Accepted for publication in ApJ