Real-time operating system support for multicore applications

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia de Automação e Sistemas, Florianópolis, 2014Plataformas multiprocessadas atuais possuem diversos níveis da memória cache entre o processador e a memória principal para esconder a latência da hierarquia de memória. O principal objetivo da hierarquia de memória é melhorar o tempo médio de execução, ao custo da previsibilidade. O uso não controlado da hierarquia da cache pelas tarefas de tempo real impacta a estimativa dos seus piores tempos de execução, especialmente quando as tarefas de tempo real acessam os níveis da cache compartilhados. Tal acesso causa uma disputa pelas linhas da cache compartilhadas e aumenta o tempo de execução das aplicações. Além disso, essa disputa na cache compartilhada pode causar a perda de prazos, o que é intolerável em sistemas de tempo real críticos. O particionamento da memória cache compartilhada é uma técnica bastante utilizada em sistemas de tempo real multiprocessados para isolar as tarefas e melhorar a previsibilidade do sistema. Atualmente, os estudos que avaliam o particionamento da memória cache em multiprocessadores carecem de dois pontos fundamentais. Primeiro, o mecanismo de particionamento da cache é tipicamente implementado em um ambiente simulado ou em um sistema operacional de propósito geral. Consequentemente, o impacto das atividades realizados pelo núcleo do sistema operacional, tais como o tratamento de interrupções e troca de contexto, no particionamento das tarefas tende a ser negligenciado. Segundo, a avaliação é restrita a um escalonador global ou particionado, e assim não comparando o desempenho do particionamento da cache em diferentes estratégias de escalonamento. Ademais, trabalhos recentes confirmaram que aspectos da implementação do SO, tal como a estrutura de dados usada no escalonamento e os mecanismos de tratamento de interrupções, impactam a escalonabilidade das tarefas de tempo real tanto quanto os aspectos teóricos. Entretanto, tais estudos também usaram sistemas operacionais de propósito geral com extensões de tempo real, que afetamos sobre custos de tempo de execução observados e a escalonabilidade das tarefas de tempo real. Adicionalmente, os algoritmos de escalonamento tempo real para multiprocessadores atuais não consideram cenários onde tarefas de tempo real acessam as mesmas linhas da cache, o que dificulta a estimativa do pior tempo de execução. Esta pesquisa aborda os problemas supracitados com as estratégias de particionamento da cache e com os algoritmos de escalonamento tempo real multiprocessados da seguinte forma. Primeiro, uma infraestrutura de tempo real para multiprocessadores é projetada e implementada em um sistema operacional embarcado. A infraestrutura consiste em diversos algoritmos de escalonamento tempo real, tais como o EDF global e particionado, e um mecanismo de particionamento da cache usando a técnica de coloração de páginas. Segundo, é apresentada uma comparação em termos da taxa de escalonabilidade considerando o sobre custo de tempo de execução da infraestrutura criada e de um sistema operacional de propósito geral com extensões de tempo real. Em alguns casos, o EDF global considerando o sobre custo do sistema operacional embarcado possui uma melhor taxa de escalonabilidade do que o EDF particionado com o sobre custo do sistema operacional de propósito geral, mostrando claramente como diferentes sistemas operacionais influenciam os escalonadores de tempo real críticos em multiprocessadores. Terceiro, é realizada uma avaliação do impacto do particionamento da memória cache em diversos escalonadores de tempo real multiprocessados. Os resultados desta avaliação indicam que um sistema operacional "leve" não compromete as garantias de tempo real e que o particionamento da cache tem diferentes comportamentos dependendo do escalonador e do tamanho do conjunto de trabalho das tarefas. Quarto, é proposto um algoritmo de particionamento de tarefas que atribui as tarefas que compartilham partições ao mesmo processador. Os resultados mostram que essa técnica de particionamento de tarefas reduz a disputa pelas linhas da cache compartilhadas e provê garantias de tempo real para sistemas críticos. Finalmente, é proposto um escalonador de tempo real de duas fases para multiprocessadores. O escalonador usa informações coletadas durante o tempo de execução das tarefas através dos contadores de desempenho em hardware. Com base nos valores dos contadores, o escalonador detecta quando tarefas de melhor esforço o interferem com tarefas de tempo real na cache. Assim é possível impedir que tarefas de melhor esforço acessem as mesmas linhas da cache que tarefas de tempo real. O resultado desta estratégia de escalonamento é o atendimento dos prazos críticos e não críticos das tarefas de tempo real.Abstracts: Modern multicore platforms feature multiple levels of cache memory placed between the processor and main memory to hide the latency of ordinary memory systems. The primary goal of this cache hierarchy is to improve average execution time (at the cost of predictability). The uncontrolled use of the cache hierarchy by realtime tasks may impact the estimation of their worst-case execution times (WCET), specially when real-time tasks access a shared cache level, causing a contention for shared cache lines and increasing the application execution time. This contention in the shared cache may leadto deadline losses, which is intolerable particularly for hard real-time (HRT) systems. Shared cache partitioning is a well-known technique used in multicore real-time systems to isolate task workloads and to improve system predictability. Presently, the state-of-the-art studies that evaluate shared cache partitioning on multicore processors lack two key issues. First, the cache partitioning mechanism is typically implemented either in a simulated environment or in a general-purpose OS (GPOS), and so the impact of kernel activities, such as interrupt handlers and context switching, on the task partitions tend to be overlooked. Second, the evaluation is typically restricted to either a global or partitioned scheduler, thereby by falling to compare the performance of cache partitioning when tasks are scheduled by different schedulers. Furthermore, recent works have confirmed that OS implementation aspects, such as the choice of scheduling data structures and interrupt handling mechanisms, impact real-time schedulability as much as scheduling theoretic aspects. However, these studies also used real-time patches applied into GPOSes, which affects the run-time overhead observed in these works and consequently the schedulability of real-time tasks. Additionally, current multicore scheduling algorithms do not consider scenarios where real-time tasks access the same cache lines due to true or false sharing, which also impacts the WCET. This thesis addresses these aforementioned problems with cache partitioning techniques and multicore real-time scheduling algorithms as following. First, a real-time multicore support is designed and implemented on top of an embedded operating system designed from scratch. This support consists of several multicore real-time scheduling algorithms, such as global and partitioned EDF, and a cache partitioning mechanism based on page coloring. Second, it is presented a comparison in terms of schedulability ratio considering the run-time overhead of the implemented RTOS and a GPOS patched with real-time extensions. In some cases, Global-EDF considering the overhead of the RTOS is superior to Partitioned-EDF considering the overhead of the patched GPOS, which clearly shows how different OSs impact hard realtime schedulers. Third, an evaluation of the cache partitioning impacton partitioned, clustered, and global real-time schedulers is performed.The results indicate that a lightweight RTOS does not impact real-time tasks, and shared cache partitioning has different behavior depending on the scheduler and the task's working set size. Fourth, a task partitioning algorithm that assigns tasks to cores respecting their usage of cache partitions is proposed. The results show that by simply assigning tasks that shared cache partitions to the same processor, it is possible to reduce the contention for shared cache lines and to provideHRT guarantees. Finally, a two-phase multicore scheduler that provides HRT and soft real-time (SRT) guarantees is proposed. It is shown that by using information from hardware performance counters at run-time, the RTOS can detect when best-effort tasks interfere with real-time tasks in the shared cache. Then, the RTOS can prevent best effort tasks from interfering with real-time tasks. The results also show that the assignment of exclusive partitions to HRT tasks together with the two-phase multicore scheduler provides HRT and SRT guarantees, even when best-effort tasks share partitions with real-time tasks

Production in Au-Au Collisions

This thesis presents the first J/ Ψ production analysis of Au+Au reactions at forward rapidity at p √sNN = 200 GeV. In the second year of RHIC running, design energy was achieved in the collisions of both Au+Au ions and proton+proton reactions. The production of the J/Ψ is measured by the PHENIX experiment in Au+Au collisions as well as in proton-proton collisions. The scientific goal is to investigate the nature of hot, dense nuclear matter capitalizing on the unique properties of the J/ Ψ as a probe of this matter. Recent experimental results by the NA50 collaboration at CERN strongly deviate from the conventional picture that successfully describes data at lower energies. The importance of such a measurement is demonstrated by the wide spectrum of theoretical explanations concerning the existing data. The merits of these models will be explored in a systematic and comprehensive study of the J/ Ψ and open charm in collisions of a variety of species and energy. A survey of the theoretical models is presented and the relevant open charm and J/ Ψ PHENIX measurements are compared

2D Static Resource Allocation for Compressed Linear Algebra and Communication Constraints

International audienceThis paper adresses static resource allocation problems for irregular distributed parallel applications. More precisely, we focus on two classical tiled linear algebra kernels: the Matrix Multiplication (MM) and the LU decomposition (LU) algorithms on large linear systems. In the context of parallel distributed platforms, data exchanges can dramatically degrade the performance of linear algebra kernels and in this context, compression techniques such as Block Low Rank (BLR) compression techniques are good candidates both for limiting data storage on each processor and data exchanges between processors. On the other hand, the use of BLR representation makes the static allocation problem of tiles to processors more complex. Indeed, the load associated to each tile depends on its compression factor, which induces an heterogeneous load balancing problem. In turn, solving this load balancing problem optimally might lead to complex allocation schemes, where the tiles allocated to a given processor are scattered all over the matrix. This in turn induces communication costs, since matrix multiplication and LU decompositions heavily rely on broadcasting operations along rows and columns of processors, so that the communication volume is minimized when the maximal number of different processors on any row and column is minimized. In the fully homogeneous case, 2D Block Cyclic (BC) allocation solves both load balancing and communication minimization issues simultaneously , but it might lead to bad load balancing in the heterogeneous case. Our goal in this paper is to propose data allocation schemes dedicated to BLR format and to prove that it is possible to obtain good performance on makespan when simultaneously balancing the load and minimizing the maximal number of different processor in any row or column

Final Targeting Strategy for the SDSS-IV APOGEE-2N Survey

APOGEE-2 is a dual-hemisphere, near-infrared (NIR), spectroscopic survey with the goal of producing a chemo-dynamical mapping of the Milky Way Galaxy. The targeting for APOGEE-2 is complex and has evolved with time. In this paper, we present the updates and additions to the initial targeting strategy for APOGEE-2N presented in Zasowski et al. (2017). These modifications come in two implementation modes: (i) "Ancillary Science Programs" competitively awarded to SDSS-IV PIs through proposal calls in 2015 and 2017 for the pursuit of new scientific avenues outside the main survey, and (ii) an effective 1.5-year expansion of the survey, known as the Bright Time Extension, made possible through accrued efficiency gains over the first years of the APOGEE-2N project. For the 23 distinct ancillary programs, we provide descriptions of the scientific aims, target selection, and how to identify these targets within the APOGEE-2 sample. The Bright Time Extension permitted changes to the main survey strategy, the inclusion of new programs in response to scientific discoveries or to exploit major new datasets not available at the outset of the survey design, and expansions of existing programs to enhance their scientific success and reach. After describing the motivations, implementation, and assessment of these programs, we also leave a summary of lessons learned from nearly a decade of APOGEE-1 and APOGEE-2 survey operations. A companion paper, Santana et al. (submitted), provides a complementary presentation of targeting modifications relevant to APOGEE-2 operations in the Southern Hemisphere.Comment: 59 pages; 11 Figures; 7 Tables; 2 Appendices; Submitted to Journal and Under Review; Posting to accompany papers using the SDSS-IV/APOGEE-2 Data Release 17 scheduled for December 202

Accurate and discernible photocollages

There currently exist several techniques for selecting and combining images from a digital image library into a single image so that the result meets certain prespecified visual criteria. Image mosaic methods, first explored by Connors and Trivedi[18], arrange library images according to some tiling arrangement, often a regular grid, so that the combination of images, when viewed as a whole, resembles some input target image. Other techniques, such as Autocollage of Rother et al.[78], seek only to combine images in an interesting and visually pleasing manner, according to certain composition principles, without attempting to approximate any target image. Each of these techniques provide a myriad of creative options for artists who wish to combine several levels of meaning into a single image or who wish to exploit the meaning and symbolism contained in each of a large set of images through an efficient and easy process. We first examine the most notable and successful of these methods, and summarize the advantages and limitations of each. We then formulate a set of goals for an image collage system that combines the advantages of these methods while addressing and mitigating the drawbacks. Particularly, we propose a system for creating photocollages that approximate a target image as an aggregation of smaller images, chosen from a large library, so that interesting visual correspondences between images are exploited. In this way, we allow users to create collages in which multiple layers of meaning are encoded, with meaningful visual links between each layer. In service of this goal, we ensure that the images used are as large as possible and are combined in such a way that boundaries between images are not immediately apparent, as in Autocollage. This has required us to apply a multiscale approach to searching and comparing images from a large database, which achieves both speed and accuracy. We also propose a new framework for color post-processing, and propose novel techniques for decomposing images according to object and texture information

Beiträge zur Zintl-Chemie der Elemente der 6. Periode im Festkörper und in Lösung

Im Rahmen der Doktorarbeit wurde die Chemie binärer Zintl-Anionen mit Trielelementen untersucht. Hierzu wurden sowohl neue Edukte zur Darstellung der Anionen als auch deren Folgechemie mit Übergangsmetallkomplexen näher betrachtet. Die Synthese des bereits in meiner Masterarbeit erstmals dargestellten Anions (TlBi3)2– konnte durch Entwicklung einer neuen Syntheseroute soweit optimiert werden, dass Umsetzungen dessen möglich wurden. Zu diesem Zweck wurde erstmals ein genauerer Blick auf die zur Synthese der Anionen verwendeten intermetallischen Verbindungen geworfen. Es zeigte sich, dass komplexe Zusammenhänge zwischen der eingangs vorgegebenen Zusammensetzung des Reaktionsgemisches, den tatsächlich erhaltenen Produkten und den daraus darstellbaren Zintl-Anionen bestehen. Aus diesem Anlass wurde eine Reihe formal ternärer intermetallischer Verbindungen dargestellt und auf ihre Bestandteile hin untersucht. Dies gelang durch die Kombination von Röntgenpulver- und Einkristalldiffraktometrie. Im Rahmen der Studien wurden Einflüsse des gewählten Alkalimetalls und die Rolle der initialen Stöchiometrie auf die Produktbildung studiert. Durch Extraktion der erhaltenen intermetallischen Verbindungen wurde eine Reihe neuer binärer Zintl-Anionen dargestellt und charakterisiert. Die Ergebnisse zeigten, dass das Anion (TlBi3)2– aus „K2TlBi3“, eigentlich einer Mischung aus KTlBi und KBi2, in hohen Ausbeuten und sehr guter Reinheit dargestellt werden kann. Die Reaktivität dessen wurde in einer Reihe von Umsetzungen mit Metallkomplexen studiert. In Reaktionen mit Lanthanoidkomplexen [Ln(cpMe4H)3] entstehen, wie im Fall der leichteren Homologen Ga und In, intermetalloide 13-Atomkäfige [Ln@Tl2Bi11]4– (Ln = La, Ce, Nd, Sm). Werden stattdessen Actinoidkomplexe [U(cpMe4H)3] oder [An(cpMe4H)3Cl] (An = U, Th) eingesetzt, entstehen wiederum 13-Atomkäfige [An@Tl2Bi11]3– (An = U, Th), die jedoch statt eines M3+-Ions ein M4+ enthalten. Diese Oxidation wurde für eine Reihe unterschiedlicher Edukte (GaBi3)2– und (Pb2Bi2)2– in Zusammenarbeit mit meinen Kollegen Armin Eulenstein und Dr. Robert J. Wilson beobachtet, woraus weitere intermetalloide Cluster [An@Bi12]q– (An/q = U/3, Th/4), [U@Pb7Bi7]3– und [An@Pb4Bi9]3– (An = U, Th) resultierten. Quantenchemische Studien deuten auf eine starke Interaktion zwischen der Clusterschale und dem Zentralatom in [An@Bi12]q– (An/q = U/3, Th/4) hin. Erstmalig wurden durch diese Synthesen intermetalloide Clusteranionen mit endohedralen Actinoidionen dargestellt und charakterisiert. In einer Reaktion von (TlBi3)2– mit [Ru(cod)(Me−Allyl)2] entstehen die Clusteranionen [Bi9{Ru(cod)}2]3– und [Tl2Bi6{Ru(cod)}]2– . Das Clusteranion [Bi9{Ru(cod)}2]3– enthält das neuartige Polybismuthidfragment Bi97– und weist eine elektronische Struktur auf, in der lokalisierte und Mehrzentrenbindungen nebeneinander vorliegen. Das Anion [Tl2Bi6{Ru(cod)}]2– war das erste ternäre Clusteranion mit Atomen der Gruppe 13, das ein d-Block-Übergangsmetallatom enthielt. Obwohl der Cluster formal die Wade-Mingos-Regeln für einen nido-Cluster erfüllt zeigen die strukturellen Parameter Auffälligkeiten, die eine nähere Betrachtung der Bindungssituation mit quantenchemischen Methoden erforderten. So zeigte sich, dass in dem (Tl2Bi6)-Fragment 2e-3c-Mehrzentrenbindungen und zu dem Ru-Atom hauptsächlich kovalente Bindungen vorliegen. Das Potential des (TlBi3)2– -Anions zur Bildung von Polybismuthiden wurde in einer Reaktionsserie mit MPh2-Komplexen (M = Zn, Cd, Hg) untersucht. Aus der Umsetzung mit CdPh2 ging die Koordinationsverbindung [(Bi7)Cd(Bi7)]4– hervor, in der zum ersten Mal das Anion Bi73- 7 als Ligand für ein Metallatom fungiert. Die Stabilität der [(Pn7)M(Pn7)]4–-Verbindungen (Pn = P - Bi, M = Zn - Hg, Hg22+) wurde mit quantenchemischen Methoden untersucht. Analoge Umsetzungen von (TlBi3)2– mit ZnPh2 und HgPh2 liefern (Tl4Bi5)3– als Hauptprodukt, im Fall von ZnPh2 gelang jedoch zusätzlich die Kristallisation eines Reaktiosintermediates. In diesem ist das Anion [(Bi6)Zn3(TlBi5)]4– zu finden, dessen elektronische Struktur mit quantenchemischen Untersuchungen näher betrachtet wurde. Diese ist, ähnlich wie im Fall von [Bi9{Ru(cod)}2]3– , komplex und es liegt wieder eine Kombination von lokalisierten und Mehrzentrenbindungen vor. Da das Anion ein fast vollständiges Bi7-Nortricyclanfragment enthält, kann es als Intermediat auf dem Weg zu dessen Bildung verstanden werden. Sowohl im Bereich der zur Synthese der binären Zintl-Anionen verwendeten Edukte als auch in den Reaktivitätsstudien wurde erst ein kleiner Einblick gewonnen. Diese Arbeit soll hierbei als Grundlage für weitere Untersuchungen in diesen Feldern dienen

PYTHIA 6.3 Physics and Manual

The PYTHIA program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, beam remnants and underlying events, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.Comment: 8 + 454 page

V0 production ratios at LHCb and the alignment of its RICH detectors

The strangeness production ratios [bar wedge]/∧ and [bar wedge]/K0S are measured by the LHCb detector from 0.3 nb-1 of proton-proton collisions delivered by the Large Hadron Collider (LHC) at CERN with centre-of-mass energy √s = 0.9TeV and 1.8 nb-1 at √s = 7TeV. Both ratios are presented as a function of transverse momentum, pT, and rapidity, y, in the ranges 0.15 < pT < 2.50 GeV/c and 2.0 < y < 4.5. The ratios measured at the two energies are in good agreement in an overlapping region of rapidity loss, Δ y = ybeam - y, and are consistent with previous measurements. A review of the Standard Model is presented with emphasis on the diffculties in its application for predictions of physics at the LHC. Phenomenological models are introduced as the current state of the art for such predictions. Accurate models are required as an essential benchmark for future discoveries of physics beyond the Standard Model. LHCb's results represent a powerful test for these models in the soft QCD regime for processes including hadronisation. The ratio [bar wedge]/∧, measuring the transport of baryon number from the collision into the detector, is smaller in data than predicted, particularly at high rapidity. The ratio [bar wedge]/K0 S, measuring the baryon-to-meson suppression in strange quark hadronisation, is significantly larger than expected. The LHCb experiment is introduced, with particular focus on its Ring Imaging Cherenkov (RICH) detectors. The development and successful implementation of a method to align those RICH detectors is presented, using proton-proton collision data from the early running period of the Large Hadron Collider, which began in November 2009. The performance of the RICH detectors is investigated with preliminary analysis of the Cherenkov photon yield. The RICH mirror positions are monitored using an automated software control system, which has been running successfully since October 2008

Dynamic recrystallization and deformation mechanisms of naturally deformed Carrara Marble: a study on one- and two-phase carbonate rocks

Carrara marble is a greenschist facies metamorphic marble from the Alpi Apuane, Tuscany, Italy. It is widely known for its chemical purity, its homogenous microstructure and isotropic texture (crystallographic preferred orientation). During two deformation events (D1 and D2) the Liassic sedimentary precursor of Carrara marble was metamorphosed and deformed. Besides statically recrystallized microstructures, two end members of dynamically recrystallized microstructures are preserved in Carrara marble (Molli et al. 1997, Molli & Heilbronner 1999, Molli et al. 2000). Both end members can be related either to sub grain rotation (SGR) recrystallization or to grain boundary migration (GBM) recrystallization, respectively. In order to characterize the different dynamically recrystallized microstructures and to relate them to mesoscopical structures of D1 and D2 a combined study of structural field geology and microstructural analysis was carried out. On the basis of a detailed structural mapping overprinting relationships between D1 and D2 were investigated and typical deformation structures were sampled. The microstructural analysis of theses shear zones and folds revealed that D1 structures are generally characterized by GBM microstructures and D2 structures by SGR microstructures. Systematic determination of deformation temperatures of D1 and D2 shear zones along a profile parallel to the main tectonic transport direction by calcite-dolomite thermometry shows two individual temperature trends for D1 and D2. The D1 deformation temperatures decrease from West to East from 430°C to 370°C and those of D2 decrease from 370°C in the East to 295°C in the West. This continuous temperature gradient makes it possible to study dynamic recrystallization microstructures over a temperature range of approximately 150°C. In order to investigate the influence of strain on the formation of microstructure and texture in naturally deformed Carrara marble a mm-scaled D2 shear zone was analyzed. The shear zone was active at a constant temperature of 325°C and cross-cut the S1 main foliation, which acted as a passive strain marker. Therefore, the observed variations of microstructure and texture are solely a function of the accommodated strain and the strain rate. The protolith is characterized by a core-mantle microstructure with coarse porphyroclasts, which are embedded in a matrix of small recrystallized grains. With increasing strain the microstructure becomes progressively recrystallized, so that the center of the shear zone is completely recrystallized and a fine-grained matrix of equally shaped recrystallized grains is developed. At the same time the texture changes from an e-twinning type (single c-axes point maximum parallel to the compression direction) in the protolith to a basal texture (single c-axes maximum perpendicular to the shear plane) in the center of the shear zone. This texture transition is caused by SGR recrystallization, which forms continuously new grains with slightly rotated crystallographic orientations in the same sense as the overall shear deformation. Strain rate estimates on the basis of experimentally derived flow laws suggest that the shear zone is highly localized in space and in time. Localization of deformation was probably caused by the presence of a pre-existing coarse-grained calcite vein. According to the Hall-Petch relationship dislocation glide is favoured by coarse-grained materials, which is why deformation may started in the vein calcite by twining. After a certain amount of strain twinning is exhausted and the deformation continued by dislocation creep associated by dynamic recrystallization. Many calcite shear zones in the Alpi Apuane contain substantial amounts of dolomite, representing a second phase in ‘pure’ Carrara marble. Second phases are considered to influence the mechanical behaviour of a mono-mineralic rock, so that the strength of the phase mixture deviates from the one of the pure end members (Tullis et al. 1991, Dresen et al. 1998, Bruhn et al. 1999). In order to investigate the influence of dolomite on microstructure, texture and the dominant deformation mechanism of calcite a shear zone from the Eastern Alpi Apuane was analyzed. The shear zone is composed of alternating calcite and dolomite rich layers. Dolomite is presumably derived from dolomite veins, which become progressively fractured and sheared so that at the highest strains completely mixed layers of calcite and dolomite are developed. Pure calcite layers are characterized by a GBM microstructure and a strong basal texture, indicating that they have deformed dominantly by dislocation creep. With increasing dolomite content the calcite grains become smaller and less lobate, while the dolomite grains maintain their initial size and shape. Also the texture of calcite becomes weaker and the initial orthorhombic symmetry (with respect to the shear plane) is almost randomized at a dolomite content of ~50 vol%. This transition suggests that the mixed layers deform dominantly by diffusion creep. Heterogeneous nucleation (Kruse & Stünitz 1999) of dolomite along calcite grain boundaries and triple junctions leads to a dispersion of calcite and dolomite, supporting the activity of diffusion creep and grain boundary sliding. The progressive addition of dolomite to calcite may lead to the transition from dislocation creep dominated deformation in the pure calcite layers to diffusion creep dominated deformation in the mixed layers. The rheological behaviour of each layer was estimated with the help of a deformation mechanism map. It turned out that the mixed layers deform either by higher strain rates and constant stresses or at lower stresses and a constant strain rate, both suggesting a localization of deformation in the mixed layers