4,631 research outputs found
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
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
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
Scalaroca stars: coupled scalar-Proca solitons
We construct and explore the physical properties of \textit{scalaroca stars}:
spherically symmetric solitonic solutions made of a complex scalar field
and a complex Proca field . We restrict our attention to configurations
in which both fields are in the fundamental state and possess an equal mass,
focusing on the cases when () the scalar and Proca fields are
(non--linearly) super--imposed and do not interact with each other; and ()
the scalar and Proca fields interact through the term . The solutions are found numerically for the non--interacting case
() as well as for both signs of the interaction coupling constant
. While pure ( single--field) Proca/scalar boson stars are the
most/least massive for weakly--interacting fields, one can obtain more massive
solutions for a sufficiently strong interaction. Besides, in the latter case,
solutions can be either in a synchronized state -- in which both fields have
the same frequency -- or in a non--synchronized state. In addition, we observe
that the coupling between the two fields allows solitonic solutions with a real
scalar field. We further comment on the possibility of spontaneous
scalarization and vectorization of the interacting solitonic solution.Comment: 21 pages, 13 figures, this project was started before the recently
published work ArXiv:2304.0801
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