The Cost of Address Translation

Modern computers are not random access machines (RAMs). They have a memory hierarchy, multiple cores, and virtual memory. In this paper, we address the computational cost of address translation in virtual memory. Starting point for our work is the observation that the analysis of some simple algorithms (random scan of an array, binary search, heapsort) in either the RAM model or the EM model (external memory model) does not correctly predict growth rates of actual running times. We propose the VAT model (virtual address translation) to account for the cost of address translations and analyze the algorithms mentioned above and others in the model. The predictions agree with the measurements. We also analyze the VAT-cost of cache-oblivious algorithms.Comment: A extended abstract of this paper was published in the proceedings of ALENEX13, New Orleans, US

Cache-Oblivious VAT-Algorithms

The VAT-model (virtual address translation model) extends the EM-model (external memory model) and takes the cost of address translation in virtual memories into account. In this model, the cost of a single memory access may be logarithmic in the largest address used. We show that the VAT-cost of cache-oblivious algorithms is only by a constant factor larger than their EM-cost; this requires a somewhat more stringent tall cache assumption as for the EM-model

A Vertical Mixture Cure Model for Credit Risk Analysis

Credit risk assessment is one of the most important tasks of banks and other financial institutions. There are three main reasons of credit termination: maturity, early repayment and default. Credits that mature can be considered as not susceptible to early termination, whereas early repayments can be treated as competing risk to default. Most credits end on time (mature) or are repaid early, default happens only for a few percentage of credits. Modelling probability of default requires taking into account the probability of early repayment and maturity. We propose the use of a vertical mixture cure model with a cured fraction to analyse the probability of default. Empirical research was conducted on the sample of 5,000 consumer credit accounts of a Polish financial institution. Credits were observed 24 months since origination. The vertical mixture cure model was estimated with characteristics of borrowers as predictors. The discrimination ability of the model through 24 months of the credit life span was compared with a mixture model that has been earlier proposed in the literature

Toward better computation models for modern machines

Modern computers are not random access machines (RAMs). They have a memory hierarchy, multiple cores, and a virtual memory. We address the computational cost of the address translation in the virtual memory and difficulties in design of parallel algorithms on modern many-core machines. Starting point for our work on virtual memory is the observation that the analysis of some simple algorithms (random scan of an array, binary search, heapsort) in either the RAM model or the EM model (external memory model) does not correctly predict growth rates of actual running times. We propose the VAT model (virtual address translation) to account for the cost of address translations and analyze the algorithms mentioned above and others in the model. The predictions agree with the measurements. We also analyze the VAT-cost of cache-oblivious algorithms. In the second part of the paper we present a case study of the design of an efficient 2D convex hull algorithm for GPUs. The algorithm is based on the ultimate planar convex hull algorithm of Kirkpatrick and Seidel, and it has been referred to as the first successful implementation of the QuickHull algorithm on the GPU by Gao et al. in their 2012 paper on the 3D convex hull. Our motivation for work on modern many-core machines is the general belief of the engineering community that the theory does not produce applicable results, and that the theoretical researchers are not aware of the difficulties that arise while adapting algorithms for practical use. We concentrate on showing how the high degree of parallelism available on GPUs can be applied to problems that do not readily decompose into many independent tasks.Moderne Computer sind keine Random Access Machines (RAMs), da ihr Speicher hierarchisch ist und sie sowohl mehrere Rechenkerne als auch virtuellen Speicher benutzen. Wir betrachten die Kosten von Adressübersetzungen in virtuellem Speicher und die Schwierigkeiten beim Entwurf nebenläufiger Algorithmen für moderne Mehrkernprozessoren. Am Anfang unserer Arbeit über virtuellen Speicher steht die Beobachtung, dass die Analyse einiger einfacher Algorithmen (zufällige Zugriffe in einem Array, Binärsuche, Heapsort) sowohl im RAM Modell als auch im EM (Modell für externen Speicher) die tatsächlichen asymptotischen Laufzeiten nicht korrekt wiedergibt. Um auch die Kosten der Adressübersetzung mit in die Analyse aufzunehmen, definieren wir das sogenannte VAT Modell (virtual address translation) und benutzen es, um die oben genannten Algorithmen zu analysieren. In diesem Modell stimmen die theoretischen Laufzeiten mit den Messungen aus der Praxis überein. Zudem werden die Kosten von Cache-oblivious Algorithmen im VAT Modell untersucht. Der zweite Teil der Arbeit behandelt eine Fallstudie zur Implementierung eines effizienten Algorithmus zur Berechnung von konvexen Hüllen in 2D auf GPUs (Graphics Processing Units). Der Algorithmus basiert auf dem ultimate planar convex hull algorithm von Kirkpatrick und Seidel und wurde 2012 von Gao et al. in ihrer Veröffentlichung über konvexe Hüllen in 3D als die erste erfolgreiche Implementierung des QuickHull-Algorithmus auf GPUs bezeichnet. Motiviert wird diese Arbeit durch den generellen Glauben der IT-Welt, dass Resultate aus der theoretischen Informatik nicht immer auf Probleme in der Praxis anwendbar sind und dass oft nicht auf die speziellen Anforderungen und Probleme eingegangen wird, die mit einer Implementierung eines Algorithmus einhergehen. Wir zeigen, wie der hohe Grad an Parallelität, der auf GPUs verfügbar ist, für Probleme nutzbar gemacht werden kann, für die eine Zerlegung in unabhängige Teilprobleme nicht offensichtlich ist

Kapitał relacyjny a wyniki ekonomiczne małych i średnich firm w Polsce

MSP odgrywają dominującą rolę w polskiej gospodarce. Sektor MSP zatrudnia 6,6 mln osób, reprezentujących 70% osób pracujących w sektorze przedsiębiorstw w Polsce. Celem niniejszego artykułu jest przedstawienie problemów MOEP w budowaniu relacji z różnych uczestników rynku, w szczególności wpływu ilości i jakości relacji na wyniki gospodarcze sektora MSP. Badanie zostało przeprowadzone w 2009 roku na losowej próbie 1346 małych i średnich przedsiębiorstw w całej Polsce. Statystyki opisowe pokazały, że dodatnie zmiany wskaźników ekonomicznych (obrotów, zysków i marży operacyjnej) notowały najczęściej firmy o większej liczbie oraz wyższej jakości relacji z otoczeniem gospodarczym. Ujemne wartości zmiany wskaźników ekonomicznych z kolei częściej wykazywały przedsiębiorstwa o bardzo niskich wskaźnikach kapitału relacyjnego

Foreign ownership as a neglected factor in regions’ smart specialisation exports

A region can internationalise in various ways. The question is what type of internationalisation at regional level can be regarded as “smart” and what role should be played in it by foreign owned entities (FOEs)? The paper aims at identifying the role played by FOEs in NUTS-2 smart specialisations’ (SS’s) internationalisation through exports. With the use of a set of PCSE regressions, the paper depicts the role of FOEs in creating SS-compliant exports against the background of their influence on total regional exports. The obtained results proved the positive role of FOEs in regional exports per se and SS-compliant exports. Yet, FOEs differed substantially, as compared to indigenous entities, in terms of product/regional specialisation and technological advancement. The findings imply the importance of FOEs’ embeddedness in regions’ economies and possibility of their incorporation in creating or enhancing regional comparative advantages. The paper contributes by: (i) providing empirical verification of one of the aspects of SS strategy which is exports and establishing comprehensive insight into the evaluation of SS, (ii) depicting the role of FOEs in generating SS-compliant exports, (iii) proposing a set of measures to be used in the extended empirical evaluation of SS consequences in the sphere of exports

A novel, nested, multiplex, real-time PCR for detection of bacteria and fungi in blood

BACKGROUND: The study describes the application of the PCR method for the simultaneous detection of DNA of Gram-negative bacteria, Gram-positive bacteria, yeast fungi and filamentous fungi in blood and, thus, a whole range of microbial etiological agents that may cause sepsis. Material for the study was sterile blood inoculated with four species of microorganisms (Escherichia coli, Staphylococcus aureus, Candida albicans and Aspergillus fumigatus) and blood collected from patients with clinical symptoms of sepsis. The developed method is based on nested-multiplex real-time PCR . RESULTS: Analysis of the obtained data shows that sensitivity of nested-multiplex real-time PCR remained at the level of 10(1) CFU/ml for each of the four studied species of microorganisms and the percentage of positive results of the examined blood samples from the patients was 70% and 19% for the microbiological culture method. The designed primers correctly typed the studied species as belonging to the groups of Gram-positive bacteria, Gram-negative bacteria, yeast fungi, or filamentous fungi. CONCLUSIONS: Results obtained by us indicated that the designed PCR methods: (1) allow to detect bacteria in whole blood samples, (2) are much more sensitive than culture method, (3) allow differentiation of the main groups of microorganisms within a few hours

Tail-Oxidized Cholesterol Enhances Membrane Permeability for Small Solutes

Cholesterol renders mammalian cell membranes more compact by reducing the amount of voids in the membrane structure. Because of this, cholesterol is known to regulate the ability of cell membranes to prevent the permeation of water and water-soluble molecules through the membranes. Meanwhile, it is also known that even seemingly tiny modifications in the chemical structure of cholesterol can lead to notable changes in membrane properties. The question is, how significantly do these small changes in cholesterol structure affect the permeability barrier function of cell membranes? In this work, we applied fluorescence methods as well as atomistic molecular dynamics simulations to characterize changes in lipid membrane permeability induced by cholesterol oxidation. The studied 7 beta-hydroxycholesterol (7 beta-OH-chol) and 27-hydroxycholesterol (27-OH-chol) represent two distinct groups of oxysterols, namely, ring- and tail-oxidized cholesterols, respectively. Our previous research showed that the oxidation of the cholesterol tail has only a marginal effect on the structure of a lipid bilayer; however, oxidation was found to disturb membrane dynamics by introducing a mechanism that allows sterol molecules to move rapidly back and forth across the membranebobbing. Herein, we show that bobbing of 27-OH-chol accelerates fluorescence quenching of NBD-lipid probes in the inner leaflet of liposomes by dithionite added to the liposomal suspension. Systematic experiments using fluorescence quenching spectroscopy and microscopy led to the conclusion that the presence of 27-OH-chol increases membrane permeability to the dithionite anion. Atomistic molecular dynamics simulations demonstrated that 27-OH-chol also facilitates water transport across the membrane. The results support the view that oxysterol bobbing gives rise to successive perturbations to the hydrophobic core of the membrane, and these perturbations promote the permeation of water and small water-soluble molecules through a lipid bilayer. The observed impairment of permeability can have important consequences for eukaryotic organisms. The effects described for 27-OH-chol were not observed for 7 beta-OH-chol which represents ring-oxidized sterols.Peer reviewe