5,714 research outputs found
Compressive and shear behaviour of masonry panels: experimentation and numerical analysis
The compressive and shear behavior of masonry is here studied both experimental- ly and numerically. An experimental campaign has been carried out on 9 square-shaped one leaf masonry panels, reproducing historical masonry. Tests have been done for evaluating the elastic and shear moduli in both plane directions, with 6 panels rotated by 90 degrees, lead- ing to vertically aligned bed joints, and 3 panels maintained with horizontal bed joints. Com- pressive tests were executed on 6 masonry panels, 3 of them rotated by 90 degrees. Initial shear strength and shear modulus parallel to bed joints are evaluated through shear tests on 9 masonry triplets. Shear tests are performed on 3 rotated panels, applying an horizontal dis- tributed load, without vertical compression. Attention is paid to the service load state: only the initial phase of the tests is studied. Numerical models are proposed for representing actu- al masonry behavior, both discrete [1] and continuous [2,3], standard and micropolar, ob- tained by homogenization procedures [4]. Several numerical analyses are performed for simulating the experimental tests on masonry triplets and panels. The mechanical elastic pa- rameters of both discrete and continuous models are calibrated starting from laboratory data of masonry constituents and then by fitting the results of the initial phases of the experimental tests on masonry specimens
Dynamical and Statistical Criticality in a Model of Neural Tissue
For the nervous system to work at all, a delicate balance of excitation and
inhibition must be achieved. However, when such a balance is sought by global
strategies, only few modes remain balanced close to instability, and all other
modes are strongly stable. Here we present a simple model of neural tissue in
which this balance is sought locally by neurons following `anti-Hebbian'
behavior: {\sl all} degrees of freedom achieve a close balance of excitation
and inhibition and become "critical" in the dynamical sense. At long
timescales, the modes of our model oscillate around the instability line, so an
extremely complex "breakout" dynamics ensues in which different modes of the
system oscillate between prominence and extinction. We show the system develops
various anomalous statistical behaviours and hence becomes self-organized
critical in the statistical sense
Context Attentive Bandits: Contextual Bandit with Restricted Context
We consider a novel formulation of the multi-armed bandit model, which we
call the contextual bandit with restricted context, where only a limited number
of features can be accessed by the learner at every iteration. This novel
formulation is motivated by different online problems arising in clinical
trials, recommender systems and attention modeling. Herein, we adapt the
standard multi-armed bandit algorithm known as Thompson Sampling to take
advantage of our restricted context setting, and propose two novel algorithms,
called the Thompson Sampling with Restricted Context(TSRC) and the Windows
Thompson Sampling with Restricted Context(WTSRC), for handling stationary and
nonstationary environments, respectively. Our empirical results demonstrate
advantages of the proposed approaches on several real-life datasetsComment: IJCAI 201
Computational Models of Adult Neurogenesis
Experimental results in recent years have shown that adult neurogenesis is a
significant phenomenon in the mammalian brain. Little is known, however, about
the functional role played by the generation and destruction of neurons in the
context of and adult brain. Here we propose two models where new projection
neurons are incorporated. We show that in both models, using incorporation and
removal of neurons as a computational tool, it is possible to achieve a higher
computational efficiency that in purely static, synapse-learning driven
networks. We also discuss the implication for understanding the role of adult
neurogenesis in specific brain areas.Comment: To appear Physica A, 7 page
Noise-induced memory in extended excitable systems
We describe a form of memory exhibited by extended excitable systems driven
by stochastic fluctuations. Under such conditions, the system self-organizes
into a state characterized by power-law correlations thus retaining long-term
memory of previous states. The exponents are robust and model-independent. We
discuss novel implications of these results for the functioning of cortical
neurons as well as for networks of neurons.Comment: 4 pages, latex + 5 eps figure
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NWA 4415 AND 4416: Two new enstatite chondrites from northwest Africa
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A new CO carbonaceous chondrite from Acfer, Algeria
Many small fragments, totally weighing 118 g were found in the Acfer area by an Italian dealer. Chondrules size and types (predominance of granular olivine type), occurrence of twinned clinoenstatite and absence of plagioclase suggested a classification as CO carbonaceous chondrite
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Textural and minerochemical features of NWA 1807 and 2180, two new CV3 chondrites from northwest Africa
A textural and minerochemical study has been performed on NWA 1807 and 2180 chondrites in order to determine sizes and typologies of chondrules, relative abundances of mineral phases, compositions of main phases and bulk oxygen isotope composition
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