Um tabuleiro de duas faces: o lúdico e o aleatório na ficção científica de Philip K. Dick

Embora apenas quatro títulos da obra de Philip K. Dick abordem o tema do acaso – Solar Lottery (escrito em 1954), The Man in the High Castle (1961), The Game Players of Titan (1963) e A Maze of Death (1968) –, este surge contudo associado, e de forma bastante coerente, a outros, como a oposição humano/inumano ou a dialéctica entre a percepção e a realidade, que são mais comummente referidos como dominantes no autor. A estratégia seguida neste artigo consiste, após uma sumária passagem pelas novelas acima referidas, na demonstração de como uma aparente dualidade no tratamento do acaso pode ser resolvida a partir do momento em que se assume uma perspectiva mais alargada do universo temático de Philip K. Dick.

GPU implementation of a hyperspectral coded aperture algorithm for compressive sensing

This paper presents a new parallel implementation of a previously hyperspectral coded aperture (HYCA) algorithm for compressive sensing on graphics processing units (GPUs). HYCA method combines the ideas of spectral unmixing and compressive sensing exploiting the high spatial correlation that can be observed in the data and the generally low number of endmembers needed in order to explain the data. The proposed implementation exploits the GPU architecture at low level, thus taking full advantage of the computational power of GPUs using shared memory and coalesced accesses to memory. The proposed algorithm is evaluated not only in terms of reconstruction error but also in terms of computational performance using two different GPU architectures by NVIDIA: GeForce GTX 590 and GeForce GTX TITAN. Experimental results using real data reveals signficant speedups up with regards to serial implementation.

Parallel hyperspectral compressive sensing method on GPU

Remote hyperspectral sensors collect large amounts of data per flight usually with low spatial resolution. It is known that the bandwidth connection between the satellite/airborne platform and the ground station is reduced, thus a compression onboard method is desirable to reduce the amount of data to be transmitted. This paper presents a parallel implementation of an compressive sensing method, called parallel hyperspectral coded aperture (P-HYCA), for graphics processing units (GPU) using the compute unified device architecture (CUDA). This method takes into account two main properties of hyperspectral dataset, namely the high correlation existing among the spectral bands and the generally low number of endmembers needed to explain the data, which largely reduces the number of measurements necessary to correctly reconstruct the original data. Experimental results conducted using synthetic and real hyperspectral datasets on two different GPU architectures by NVIDIA: GeForce GTX 590 and GeForce GTX TITAN, reveal that the use of GPUs can provide real-time compressive sensing performance. The achieved speedup is up to 20 times when compared with the processing time of HYCA running on one core of the Intel i7-2600 CPU (3.4GHz), with 16 Gbyte memory.

Parallel hyperspectral coded aperture for compressive sensing on GPUs

The application of compressive sensing (CS) to hyperspectral images is an active area of research over the past few years, both in terms of the hardware and the signal processing algorithms. However, CS algorithms can be computationally very expensive due to the extremely large volumes of data collected by imaging spectrometers, a fact that compromises their use in applications under real-time constraints. This paper proposes four efficient implementations of hyperspectral coded aperture (HYCA) for CS, two of them termed P-HYCA and P-HYCA-FAST and two additional implementations for its constrained version (CHYCA), termed P-CHYCA and P-CHYCA-FAST on commodity graphics processing units (GPUs). HYCA algorithm exploits the high correlation existing among the spectral bands of the hyperspectral data sets and the generally low number of endmembers needed to explain the data, which largely reduces the number of measurements necessary to correctly reconstruct the original data. The proposed P-HYCA and P-CHYCA implementations have been developed using the compute unified device architecture (CUDA) and the cuFFT library. Moreover, this library has been replaced by a fast iterative method in the P-HYCA-FAST and P-CHYCA-FAST implementations that leads to very significant speedup factors in order to achieve real-time requirements. The proposed algorithms are evaluated not only in terms of reconstruction error for different compressions ratios but also in terms of computational performance using two different GPU architectures by NVIDIA: 1) GeForce GTX 590; and 2) GeForce GTX TITAN. Experiments are conducted using both simulated and real data revealing considerable acceleration factors and obtaining good results in the task of compressing remotely sensed hyperspectral data sets.

Anisotropy effects during unstable step flow growth

Step flow growth, meandering instability, coarsening

Nutrition et Cerveau

L'énergie requise pour assurer un fonctionnement cérébral adéquat est considérable, et la synthèse et l'acheminement des nutriments sont largement tributaires de l'apport alimentaire. A l'inverse, le cerveau est nécessaire à la régulation de la prise de nourriture, soulignant son Interdépendance avec la nutrition. Bien que plus résistant à un apport calorique réduit que la majorité des autres organes, il peut souffrir de carences diverses, et également en être la cause. Cet article discute les mécanismes impliqués dans la régulation de la prise d'aliments, au travers d'exemples tels que les troubles du comportement alimentaire. Les carences vitaminiques et les régimes amaigrissants sont discutés à la lumière des conséquences neurologiques qu'ils entraînent.

Mieux connaître la médecine du travail

Les Suisses travaillent... et consultent leur médecin. La Suisse est un pays de travailleurs: un des taux de chômage les plus bas du monde (moins de 5 %), 4,4 millions de personnes actives professionnellement sur 7,5 millions d'habitants... Et, heureusement, de travailleurs sains pour la plupart: selon une enquête de 2002, 85 % des Suisses de quinze ans et plus s'estimaient en bonne santé. Malgré cela, 77 % d'entre eux avaient tout de même eu recours à un médecin dans les douze mois précédant l'enquête. Si l'on ne retient que les personnes de 15 à 64 ans (donc professionnellement actives pour la plupart), la proportion se monte même à 81 %, ce qui représente près de deux millions de personnes ayant consulté au minimum une fois dans l'année. [Auteurs]

Acquisitions thérapeutiques 2003: Neurologie

Cet article présente les principales acquisitions thérapeutiques 2003 dans le domaine de la neurologie. L'accent est mis sur les implications pour la pratique clinique quotidienne, avec des recommandations basées autant que possible sur des preuves (evidence-based). Dans les maladies cérébrovasculaires et dans les démences, les résultats de plusieurs études randomisées suggèrent qu'il faut parfois traiter les patients avec des antihypertenseurs et des hypolipémiants, même s'ils ne sont ni hypertendus ni hypercholestérolémiques. L'acquisition principale dans le domaine de la sclérose en plaques est l'homologation de la mitoxantrone au printemps dernier, pour les formes graves de la maladie. Des progrès ont été réalisés dans le traitement de certaines formes de dystrophies musculaires, et des méta-analyses ont permis de clarifier l'efficacité des traitements dans les polyradiculoneuropathies inflammatoires. L'évolution de la prise en charge des mouvements anormaux est marquée par l'essor de la stimulation cérébrale profonde.

The second law of thermodynamics and the global climate system : A review of the maximum entropy production principle

The long-term mean properties of the global climate system and those of turbulent fluid systems are reviewed from a thermodynamic viewpoint. Two general expressions are derived for a rate of entropy production due to thermal and viscous dissipation (turbulent dissipation) in a fluid system. It is shown with these expressions that maximum entropy production in the Earth s climate system suggested by Paltridge, as well as maximum transport properties of heat or momentum in a turbulent system suggested by Malkus and Busse, correspond to a state in which the rate of entropy production due to the turbulent dissipation is at a maximum. Entropy production due to absorption of solar radiation in the climate system is found to be irrelevant to the maximized properties associated with turbulence. The hypothesis of maximum entropy production also seems to be applicable to the planetary atmospheres of Mars and Titan and perhaps to mantle convection. Lorenz s conjecture on maximum generation of available potential energy is shown to be akin to this hypothesis with a few minor approximations. A possible mechanism by which turbulent fluid systems adjust themselves to the states of maximum entropy production is presented as a selffeedback mechanism for the generation of available potential energy. These results tend to support the hypothesis of maximum entropy production that underlies a wide variety of nonlinear fluid systems, including our planet as well as other planets and stars