High-Performance Computer Algebra: A Hecke Algebra Case Study

We describe the first ever parallelisation of an algebraic computation at modern HPC scale. Our case study poses challenges typical of the domain: it is a multi-phase application with dynamic task creation and irregular parallelism over complex control and data structures. Our starting point is a sequential algorithm for finding invariant bilinear forms in the representation theory of Hecke algebras, implemented in the GAP computational group theory system. After optimising the sequential code we develop a parallel algorithm that exploits the new skeleton-based SGP2 framework to parallelise the three most computationally-intensive phases. To this end we develop a new domain-specific skeleton, parBufferTryReduce. We report good parallel performance both on a commodity cluster and on a national HPC, delivering speedups up to 548 over the optimised sequential implementation on 1024 cores

Hole concentration and phonon renormalization in Ca-doped YBa_2Cu_3O_y (6.76 < y < 7.00)

In order to access the overdoped regime of the YBa_2Cu_3O_y phase diagram, 2% Ca is substituted for Y in YBa_2Cu_3O_y (y = 7.00,6.93,6.88,6.76). Raman scattering studies have been carried out on these four single crystals. Measurements of the superconductivity-induced renormalization in frequency (Delta \omega) and linewidth (\Delta 2\gamma) of the 340 cm^{-1} B_{1g} phonon demonstrate that the magnitude of the renormalization is directly related to the hole concentration (p), and not simply the oxygen content. The changes in \Delta \omega with p imply that the superconducting gap (\Delta_{max}) decreases monotonically with increasing hole concentration in the overdoped regime, and \Delta \omega falls to zero in the underdoped regime. The linewidth renormalization \Delta 2\gamma is negative in the underdoped regime, crossing over at optimal doping to a positive value in the overdoped state.Comment: 18 pages; 5 figures; submitted to Phys. Rev. B Oct. 24, 2002 (BX8292

Light induced defects in thermal annealed hydrogenated amorphous silicon

The metastable defects of a-Si:H samples annealed at temperatures in the 300-550°C range have been studied by photothermal deflection spectroscopy (PDS). The light-soaked samples show an increase in optical absorption in the 0.8 to 1.5 eV range. The metastable defect density decreases when the annealing temperature increases, while the defect density increases. This decrease in the metastable defect density shows an almost linear correlation with the decrease in the hydrogen content of the samples, determined by IR transmission spectroscopy and thermal desorption spectroscopy

[Small cell lung cancer and immuno-oncologic agents: End of the cisplatin - etoposide era?]

International audienceIn the setting of small cell lung cancer (SCLC), the development of immuno-oncological agents, particularly those targeting Programmed cell Death protein 1 (PD-1) and Programmed cell Death protein Ligand 1 (PD-L1), is still at an early stage. Two critical elements need to be considered : the current data are extracted from Phase I and Phase II trials and the level of evidence from phase III trials has not been reached as it has been for non-small cell lung cancer (NSCLC) or for malignant melanoma ; The second aspect is the slow development of predictive factors for response to the immuno-oncological agents targeting the PD-1 receptor and its ligand. The clinical data are still too fragmentary to produce recommendations, although the improvement in progression-free survival seen in different phase II studies is promising. The expectation of clinicians dealing withSCLC is an indication of the challenge that this disease currently poses to oncology and justifies a focused clinical research effort

Regular Versus Irregular Problems and Algorithms.

. Viewing a parallel execution as a set of tasks that execute on a set of processors, a main problem is to find a schedule of the tasks that provides an efficient execution. This usually leads to divide algorithms into two classes: static and dynamic algorithms, depending on whether the schedule depends on the indata or not. To improve this rough classification we study, on some key applications of the Stratag` eme project [21, 22], the different ways schedules can be obtained and the associated overheads. This leads us to propose a classification based on regularity criteria i.e. measures of how much an algorithm is regular (or irregular). For a given algorithm, this expresses more the quality of the schedules that can be found (irregular versus regular) as opposed to the way the schedules are obtained (dynamic versus static). These studies reveal some paradigms of parallel programming for irregular algorithms. Thus, in a second part we study a parallel programming model that takes i..

L'accueil de projets exogènes à l'IEMN dans le cadre du réseau RTB du CNRS

International audienc

The peptide sequence Arg-Glu-Arg, present in the amyloid precursor protein, protects against memory loss caused by Aβ and acts as a cognitive enhancer

Amino acid sequences containing the palindromic tripeptide RER, matching amino acids 328-330 of the amyloid precursor protein APP, when injected intracerebrally prior to or just after training, protect against memory loss induced by amyloid-beta (Aβ) in a one-trial passive avoidance task in the young chick. RER also acts as a cognitive enhancer, strengthening memory for a weak version of the task. N-terminal acylation of RER protects it against rapid degradation, and Ac-RER is effective in restoring memory if administered peripherally. Biotinylated RER binds to chick neuronal perikarya in an APP-displaceable manner via 66 and ~110 kDa neuronal cell membrane proteins. We suggest that RER binding is likely to exert effects on memory retention via receptor-mediated events that include activation of second messenger pathways. These findings suggest that RER and its derivatives may offer a novel approach to enhancing the neuroprotective effects of APP and alleviating the effects of memory loss in the early stages of Alzheimer’s disease