Fault-Aware Non-Collective Communication Creation and Reparation in MPI

The increasing size of HPC architectures makes the faults' presence a more and more frequent eventuality. This issue becomes especially relevant since MPI, the de-facto standard for inter-process communication, lacks proper fault management functionalities. Past efforts produced extensions to the MPI standard that enabled fault management, including ULFM. While providing powerful tools to handle faults, it still faces limitations like the collectiveness of the repair procedure. With this paper, we overcome those limitations and achieve fault-aware non-collective communicator creation and reparation. We integrate our solution into an existing fault resiliency framework and measure the overhead introduced in the application code. The experimental campaign shows that our solution is scalable and introduces a limited overhead, and the non-collective reparation is a viable opportunity for ULFM-based applications

Legio: Fault Resiliency for Embarrassingly Parallel MPI Applications

Due to the increasing size of HPC machines, the fault presence is becoming an eventuality that applications must face. Natively, MPI provides no support for the execution past the detection of a fault, and this is becoming more and more constraining. With the introduction of ULFM (User Level Fault Mitigation library), it has been provided with a possible way to overtake a fault during the application execution at the cost of code modifications. ULFM is intrusive in the application and requires also a deep understanding of its recovery procedures. In this paper we propose Legio, a framework that lowers the complexity of introducing resiliency in an embarrassingly parallel MPI application. By hiding ULFM behind the MPI calls, the library is capable to expose resiliency features to the application in a transparent manner thus removing any integration effort. Upon fault, the failed nodes are discarded and the execution continues only with the non-failed ones. A hierarchical implementation of the solution has been also proposed to reduce the overhead of the repair process when scaling towards a large number of nodes. We evaluated our solutions on the Marconi100 cluster at CINECA, showing that the overhead introduced by the library is negligible and it does not limit the scalability properties of MPI. Moreover, we also integrated the solution in real-world applications to further prove its robustness by injecting faults

Fault Awareness in the MPI 4.0 Session Model

The latest version of MPI introduces new functionalities like the Session model, but it still lacks fault management mechanisms. Past efforts produced tools and MPI standard extensions to manage fault presence, including ULFM. These measures are effective against faults but do not fully support the new additions to the standard. In this paper, we combine the fault management possibilities of ULFM with the new Session model functionality introduced in version 4.0 of the standard. We focus on the communicator creation procedure, highlighting criticalities and proposing a method to circumvent them. The experimental campaign shows that the proposed solution does not significantly affect applications' execution time and scalability while better managing the insurgence of faults

Action and non-action oriented body representations. insight from behavioural and grey matter modifications in individuals with lower limb amputation

Following current model of body representations, we aimed to systematically investigate the association between brain modifications, in terms of grey matter loss, and body representation deficits, in terms of alterations of the body schema (BS) and of non-action oriented body representations (NA), in individuals with lower limb amputation (LLA)

Caracterização geoquímica e mineralógica de uma seção ao longo da laterita niquelífera da Fazenda da Roseta, Liberdade, Minas Gerais

Estudos geoquímicos e mineralógicos empreendidos ao longo de uma seção do perfil laterítico niquelífero da Fazenda da Roseta, Liberdade, Sul de Minas Gerais, revelaram teores significativos tanto na zona saprolítica (minério tipo A) quanto no horizonte oxidado (minério tipo C). O minério tipo A, bem definido no 1,5 m inferior da seção, contém teores da ordem de 1,7 wt.% NiO, com minerais garnieríticos amorfos, além de clorita e provavelmente serpentina, como fases niquelíferas. Um intervalo de cerca de 2 m define uma zona transicional do minério silicático para o oxidado, caracterizado por gradual absorção de blocos residuais da rocha parental em um plasma goetítico. Impregnações e veios de asbolano em stockwork, em consonância com anomalias de Mn e Co, delineiam o limite externo dessa zona. Baseado no conteúdo em Ni, o minério oxidado estende-se por aproximadamente 4 m. Teores médios giram em torno de 1,2 wt.% NiO, em que goetita é o principal hospedeiro de Ni, além de talco secundário. Desde a porção mais interna da seção, observa-se que o Ni é continuamente lixiviado. Assinaturas geoquímicas anômalas podem indicar a ocorrência de diques de rochas exóticas cortando o regolito. A ausência de esmectitas demonstra que condições de fluxo hídrico ativas prevaleceram durante o desenvolvimento do perfil, fato corroborado pela substituição de caolinita por gibsita, implicando condições de hidrólise severas. Veios de caolinita na zona de gibsita sugerem origem pós-laterítica. A gênese do perfil define uma evolução em pH de levemente alcalino nos estágios iniciais (associação quartzo-caolinita-zeólita) para ligeiramente ácido nas fases mais avançadas (presença de goetita aluminosa). Geochemical and mineralogical studies undertaken through a section of the nickeliferous laterite profile in Fazenda da Roseta, Liberdade, Southern Minas Gerais, revealed mineable grades, both in the saprolitic horizon (A-type ore) and in the oxidized one (C-type ore). The A-type ore, well defined in the innermost 1.5 m of the section, boasts representative grades at the order of 1.7 wt.% NiO, with amorphous garnierite-type minerals, besides chlorite and likely serpentine, as the Ni-rich phases. An approximately 2 m-long interval defines a transitional zone from the silicatic toward the oxidized ore, marked by the outward gradual absorption of residual blocks from the parent rock within a goethitic plasma. Impregnations and stockwork-like veins of asbolane, confirmed by local Mn and Co anomalies, delineate the outer edge of this zone. The oxidized ore stretches, based on Ni contents, for roughly 4 m. Average grades lie about 1.2 wt.% NiO, containing goethite as the main Ni ore mineral, plus some secondary talc. Ever since the innermost part of the section, Ni has been continuously washed away, in such a manner that its concentrations become rather low in the outermost part. Anomalous geochemical signatures may indicate the occurrence of dykes of uncommon igneous rocks crosscutting the profile. The absence of smectites in the profile points out that free flow conditions have prevailed, which is reinforced by the substitution of kaolinite by gibbsite, which highlights severe hydrolysis conditions (tendency to alitization). Kaolinite veins in the gibbsite-only zone suggest post-lateritic origin. The laterite development determines an evolution in pH conditions from slightly alkaline in the early stages (quartz–kaolinite–zeolite association) to mildly acidic in the more advanced phases (presence of Al-goethites)

Graphene glial-interfaces: challenges and perspectives

Graphene nanosheets are mechanically strong but flexible, electrically conductive and bio-compatible. Thus, due to these unique properties, they are being intensively studied as materials for the next generation of neural interfaces. Most of the literature focused on optimizing the interface between these materials and neurons. However, one of the most common causes of implant failure is the adverse inflammatory reaction of glial cells. These cells are not, as previously considered, just passive and supportive cells, but play a crucial role in the physiology and pathology of the nervous system, and in the interaction with implanted electrodes. Besides providing structural support to neurons, glia are responsible for the modulation of synaptic transmission and control of central and peripheral homeostasis. Accordingly, knowledge on the interaction between glia and biomaterials is essential to develop new implant-based therapies for the treatment of neurological disorders, such as epilepsy, brain tumours, and Alzheimer's and Parkinson's disease. This work provides an overview of the emerging literature on the interaction of graphene-based materials with glial cells, together with a complete description of the different types of glial cells and problems associated with them. We believe that this description will be important for researchers working in materials science and nanotechnology to develop new active materials to interface, measure and stimulate these cells

A computational platform for the virtual unfolding of Herculaneum Papyri

Ancient Herculaneum papyrus scrolls, hopelessly charred in the 79 A.D. Vesuvius eruption, contain valuable writings of the Greek philosophers of the day, including works of the Epicurean Philodemus. X-ray phase contrast tomography has recently begun unlocking their secrets. However, only small portions of the text hidden inside the scroll have been recover. One of the challenging tasks in Herculaneum papyri investigation is their virtual unfolding because of their highly complicated structure and three-dimensional arrangement. Although this procedure is feasible, problems in segmentation and flattening hinder the unrolling of a large portion of papyrus. We propose a computational platform for the virtual unfolding procedure, and we show the results of its application on two Herculaneum papyrus fragments. This work paves the way to a comprehensive survey and to further interpretation of larger portions of text hidden inside the carbonized Herculaneum papyri