36,308 research outputs found
A Holistic Approach to Log Data Analysis in High-Performance Computing Systems: The Case of IBM Blue Gene/Q
The complexity and cost of managing high-performance computing
infrastructures are on the rise. Automating management and repair through
predictive models to minimize human interventions is an attempt to increase
system availability and contain these costs. Building predictive models that
are accurate enough to be useful in automatic management cannot be based on
restricted log data from subsystems but requires a holistic approach to data
analysis from disparate sources. Here we provide a detailed multi-scale
characterization study based on four datasets reporting power consumption,
temperature, workload, and hardware/software events for an IBM Blue Gene/Q
installation. We show that the system runs a rich parallel workload, with low
correlation among its components in terms of temperature and power, but higher
correlation in terms of events. As expected, power and temperature correlate
strongly, while events display negative correlations with load and power. Power
and workload show moderate correlations, and only at the scale of components.
The aim of the study is a systematic, integrated characterization of the
computing infrastructure and discovery of correlation sources and levels to
serve as basis for future predictive modeling efforts.Comment: 12 pages, 7 Figure
BPS black holes, the Hesse potential, and the topological string
The Hesse potential is constructed for a class of four-dimensional N=2
supersymmetric effective actions with S- and T-duality by performing the
relevant Legendre transform by iteration. It is a function of fields that
transform under duality according to an arithmetic subgroup of the classical
dualities reflecting the monodromies of the underlying string compactification.
These transformations are not subject to corrections, unlike the
transformations of the fields that appear in the effective action which are
affected by the presence of higher-derivative couplings. The class of actions
that are considered includes those of the FHSV and the STU model. We also
consider heterotic N=4 supersymmetric compactifications. The Hesse potential,
which is equal to the free energy function for BPS black holes, is manifestly
duality invariant. Generically it can be expanded in terms of powers of the
modulus that represents the inverse topological string coupling constant,
, and its complex conjugate. The terms depending holomorphically on
are expected to correspond to the topological string partition function and
this expectation is explicitly verified in two cases. Terms proportional to
mixed powers of and are in principle present.Comment: 28 pages, LaTeX, added comment
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Experimental and Numerical Analysis of Single Phase Flow in a micro T-junction
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.In this work the fluid-dynamic behaviour of a micro T-junction has been investigated both
numerically and experimentally for low Reynolds numbers (Re<14) with water as working fluid. The
velocity profiles within the T-junction has been experimentally determined by using the micro Particle Image
Velocimetry (ÎĽPIV). The experimental data have been compared with the numerical results obtained by
means of a 3D model implemented in Comsol Multiphysics® environment for incompressible, isothermal,
laminar flows with constant properties. The comparison between the experimental and the numerical data
puts in evidence a perfect agreement among the results. In the central region of the T-junction where the
velocity profiles of the inlet branches interact, the maximum difference is less than 5.8% for different flow
rates imposed at the inlet (with the ratio 1:2) and less than 4.4% in the case of the same flow rate at the inlets
(1:1). Since the estimated uncertainty of the experimental velocity is about 3%, the obtained result can be
considered very good and it demonstrates that no significant scaling effects influences the liquid mixing for
low Reynolds numbers (Re<14) and the behaviour of the micro T-junction can be considered as
conventional. The detailed analysis of the velocity profile evolution within the central region of the mixer
has allowed to determine where the fully developed laminar profile is reached (for instance 260 mm far from
the centre of the T-junction when a maximum water flow rate of 8 ml/h is considered)
A new mechanism for spatial pattern formation via lateral and protrusion-mediated lateral signalling
Tissue organization and patterning are critical during development when genetically identical cells take on different fates. Lateral signalling plays an important role in this process by helping to generate self-organized spatial patterns in an otherwise uniform collection of cells. Recent data suggest that lateral signalling can be mediated both by junctional contacts between neighbouring cells and via cellular protrusions that allow non-neighbouring cells to interact with one another at a distance. However, it remains unclear precisely how signalling mediated by these distinct types of cell-cell contact can physically contribute to the generation of complex patterns without the assistance of diffusible morphogens or pre-patterns. To explore this question, in this work we develop a model of lateral signalling based on a single receptor/ligand pair as exemplified by Notch and Delta. We show that allowing the signalling kinetics to differ at junctional versus protrusion-mediated contacts, an assumption inspired by recent data which show that the cleavage of Notch in several systems requires both Delta binding and the application of mechanical force, permits individual cells to act to promote both lateral activation and lateral inhibition. Strikingly, under this model, in which Delta can sequester Notch, a variety of patterns resembling those typical of reaction-diffusion systems is observed, together with more unusual patterns that arise when we consider changes in signalling kinetics, and in the length and distribution of protrusions. Importantly, these patterns are self-organizing-so that local interactions drive tissue-scale patterning. Together, these data show that protrusions can, in principle, generate different types of patterns in addition to contributing to long-range signalling and to pattern refinement
Enhancing data security in cloud using random pattern fragmentation and a distributed nosql database
© 2019 IEEE. The cloud computing model has become very popular among users, as it has proven to be a cost-effective solution to store and process data, thanks to recent advancements in virtualization and distributed computing. Nevertheless, in the cloud environment, the user entrusts the safekeeping of its data entirely to the provider, which introduces the problem of how secure such data is and whether its integrity has been maintained. This paper proposes an approach to the data security in cloud by utilizing a random pattern fragmentation algorithm and combining it with a distributed NoSQL database. This not only increases the security of the data by storing it in different nodes and scramble all the bytes, but also allows the user to implement an alternative method of securing data. The performance of the approach is compared to other approaches, along with AES 256 encryption. Results indicate a significant performance improvement over encryption, highlighting the capabilities of this method for cloud stored data, as it creates a layer of protection without additional overhead
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Trace chemical measurements from the northern midlatitude lowermost stratosphere in early spring: Distributions, correlations, and fate
In situ measurements of a large number of trace chemicals from the midlatitude (37-57°N) lower stratosphere were performed with the NASA DC-8 aircraft during March 1994. Deepest penetrations into the stratosphere (550 ppb O3, 279 ppb N2O, and 350 K potential temperature) corresponded to a region that has been defined as the "lowermost stratosphere" (LS) by Holton et al [1995]. Analysis of data shows that the mixing ratios of long-lived tracer species (e. g. CH4, HNO3, NOy, CFCs) are linearly correlated with those of O3 and N2O. A ΔNOy/ΔO3 of 0.0054 ppb/ppb and ΔNOy/ΔN2O of -0.081 ppb/ppb is in good agreement with other reported measurements from the DC-8. These slopes are however, somewhat steeper than those reported from the ER-2 airborne studies. We find that the reactive nitrogen budget in the LS is largely balanced with HNO3 accounting for 80% of NOy, and PAN and NOx together accounting for 5%. A number of oxygenated species (e. g. acetone, H2O2) were present and may provide an important in situ source of HOx in the LS. SO2 mixing ratios were found to increase in the stratosphere at a rate that was comparable to the decline in OCS levels. No evidence of particle formation could be observed. Ethane, propane, and acetylene mixing ratios declined rapidly in the LS with Cl atoms likely playing a key role in this process. A number of reactive hydrocarbons/halocarbons (e. g. C6H6, CH3I) were present at low but measurable concentrations
A spatial variation model of white matter microstructure
In this study, we introduce a new technique to model the variation of microstructural parameters across speci c brain regions. We use a simple model of di usion in each voxel, but model the variation of parameters across the region using penalised splines. We t the whole region model directly to the di usion-weighted signals. We test the tech- nique on the mid-sagittal section of the corpus callosum (CC) using a di usion MRI data set with distinct age groups. The method detects di erences and separates the groups
Blueshifted galaxies in the Virgo Cluster
We examine a sample of 65 galaxies in the Virgo cluster with negative radial
velocities relative to the Local Group. Some features of this sample are
pointed out. All of these objects are positioned compactly within a virial zone
of radius 6{\deg} in the cluster, but their centroid is displaced relative to
the dynamic center of the cluster, M87, by 1.1{\deg} to the northwest. The
dwarf galaxies in this sample are clumped on a scale of ~10' (50 kpc). The
observed asymmetry in the distribution of the blueshifted galaxies may be
caused by infall of a group of galaxies around M86 onto the main body of the
cluster. We offer another attempt to explain this phenomenon, assuming a mutual
tangential velocity of ~300 km/s between the Local Group and the Virgo cluster
owing to their being repelled from the local cosmological void.Comment: 10 pages, 4 figures, 1 table. Published in Astrophysics, Vol. 53, No.
1, pp. 32-41, 201
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