Finding patterns in timed data with spike timing dependent plasticity

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.My research focuses on finding patterns in events - in sequences of data that happen over time. It takes inspiration from a neuroscience phenomena believed to be deeply involved in learning. I propose a machine learning algorithm that finds patterns in timed data and is highly robust to noise and missing data. It can find both coincident relationships, where two events tend to happen together; as well as causal relationships, where one event appears to be caused by another. I analyze stock price information using this algorithm and strong relationships are found between companies within the same industry. In particular, I worked with 12 stocks taken from the banking, information technology, healthcare, and oil industries. The relationships are almost exclusively coincidental, rather than causal.by Alexandre Oliveira.M.Eng

The nature of the LINER in the galaxy NGC 404

NGC 404, at a distance of 3.4 Mpc, is the nearest S0 galaxy. This galaxy harbors a LINER; however, since the spectrum does not show a broad H{\alpha} emission, it is not certain that this LINER is a low luminosity AGN and its nature is still an open question. HST observations show the existence of stellar populations with an age of 3 x 10^8 years years in the galactic bulge and with an age of 6-15 x 10^9 years in the galactic disk. In this work, we present an analysis of the data cube of NGC 404 obtained with the IFU (Integral Field Unity) of the GMOS (Gemini Multi-Object Spectrograph) on the Gemini North telescope.Comment: 2 pages, 2 figure

Random-energy model in random fields

The random-energy model is studied in the presence of random fields. The problem is solved exactly both in the microcanonical ensemble, without recourse to the replica method, and in the canonical ensemble using the replica formalism. The phase diagrams for bimodal and Gaussian random fields are investigated in detail. In contrast to the Gaussian case, the bimodal random field may lead to a tricritical point and a first-order transition. An interesting feature of the phase diagram is the possibility of a first-order transition from paramagnetic to mixed phase.Comment: 18 pages, 5 figures (included

Spontaneous vectorization of electrically charged black holes

In this work, we generalise the spontaneous scalarization phenomena in Einstein-Maxwell-Scalar models to a higher spin field. The result is an Einstein-Maxwell-Vector model wherein a vector field is non-minimally coupled to the Maxwell invariant by an exponential coupling function. We show that the latter guarantees the circumvention of an associated no-hair theorem when the vector field has the form of an electric field. Different than its scalar counterpart, the new spontaneously vectorized ReissnerNordstr¨om (RN) black holes are, always, undercharged while being entropically preferable. The solution profile and domain of existence are presented and analysed.publishe