arXiv subjects

Gerald Cooray

Publications and source records attributed to Gerald Cooray.

6 recordsLinked to original sources

arXiv2024

Localising the Seizure Onset Zone from Single-Pulse Electrical Stimulation Responses with a CNN Transformer

Epilepsy is one of the most common neurological disorders, often requiring surgical intervention when medication fails to control seizures. For effective surgical outcomes, precise localisation of the epileptogenic focus - often approximated through the Seizure Onset Zone (SOZ) - is critical yet remains a challenge. Active probing through electrical stimulation is already standard clinical practice for identifying epileptogenic areas. Our study advances the application of deep learning for SOZ localisation using Single-Pulse Electrical Stimulation (SPES) responses, with two key contributions. Firstly, we implement an existing deep learning model to compare two SPES analysis paradigms: divergent and convergent. These paradigms evaluate outward and inward effective connections, respectively. We assess the generalisability of these models to unseen patients and electrode placements using held-out test sets. Our findings reveal a notable improvement in moving from a divergent (AUROC: 0.574) to a convergent approach (AUROC: 0.666), marking the first application of the latter in this context. Secondly, we demonstrate the efficacy of CNN Transformers with cross-channel attention in handling heterogeneous electrode placements, increasing the AUROC to 0.730. These findings represent a significant step in modelling patient-specific intracranial EEG electrode placements in SPES. Future work will explore integrating these models into clinical decision-making processes to bridge the gap between deep learning research and practical healthcare applications.

cs.LG↗

arXiv2024

Does light slowdown in dielectric media?

Observations and theoretical principles suggest that electromagnetic waves, including light, travel more slowly in dielectric media than in vacuum. Maxwell's equations, incorporating material dependent permittivity and permeability, elegantly capture this effect. Previous studies indicate that the observed slower speed is due to interference effects, with the actual electromagnetic fields in the dielectric propagating at the speed of light in vacuum. However, these studies did not provide explicit expressions for the field components moving at this speed. The aim of the present study is to address this gap by analysing the structure of the electromagnetic field components within the dielectric. We examine how these components, each traveling at the speed of light in vacuum, interact to produce a net field that appears to propagate more slowly. Our findings show that the observed slower propagation in dielectric media results from interference between two types of waves: a forward moving incident wave and a set of secondary waves, moving both in the forward and backward directions, and induced by the interaction of the incident wave with the dielectric medium. Both the incident wave and the secondary waves travel at the speed of light in vacuum. Importantly, we observe that the reflected wave caused by the impedance discontinuity at the boundary of the dielectric medium arises from secondary waves moving in the direction opposite to the incident wave.

physics.optics↗

arXiv2022

Hints of the Photonic Nature of the Electromagnetic fields in Classical Electrodynamics and its connection to the electronic charge and vacuum energy density

The electromagnetic fields of a long dipole working without dispersive and dissipative losses are analyzed in the frequency domains. The dipole produces radiation in bursts of duration T/2 where T is the period of oscillation. The parameter studied in this paper is the energy, U, dissipated in a single burst of radiation of duration T/2. We have studied how U vary as a function of the charge associated with the current in the dipole and the ratio of the length of the dipole and its radius. We have observed a remarkable result when this ratio is equal to the ratio of the radius of the universe to the Bohr radius. Our results, based purely on the classical electrodynamics and general relativity, show that, as the magnitude of the oscillating charge (as defined by the root mean square) reduces to the electronic charge, the energy dissipated in a single burst of radiation reduces to hv, where v is the frequency of oscillation and h is the Planck constant. The importance of this finding is discussed. In particular, the results show that the existence of a minimum free charge in nature, i.e., electronic charge, is a direct consequence of the photonic nature of the electromagnetic fields. Furthermore, the presented findings allow to derive for the first time an expression for the vacuum energy density of the universe in terms of the other fundamental constants in nature, the prediction of which is consistent with experimental observations. This equation, which combines the vacuum energy, electronic charge and mass, speed of light, gravitational constant and Planck constant, creates a link between classical field theories (i.e., classical electrodynamics and general relativity) and quantum mechanics.

physics.class-ph↗

arXiv2022

Global dynamics of neural mass models

Neural mass models are used to simulate cortical dynamics and to explain the electrical and magnetic fields measured using electro- and magnetoencephalography. Simulations evince a complex phase-space structure for these kinds of models; including stationary points and limit cycles and the possibility for bifurcations and transitions among different modes of activity. This complexity allows neural mass models to describe the itinerant features of brain dynamics. However, expressive, nonlinear neural mass models are often difficult to fit to empirical data without additional simplifying assumptions: e.g., that the system can be modelled as linear perturbations around a fixed point. In this study we offer a mathematical analysis of neural mass models, specifically the canonical microcircuit model, providing analytical solutions describing dynamical itinerancy. We derive a perturbation analysis up to second order of the phase flow, together with adiabatic approximations. This allows us to describe amplitude modulations as gradient flows on a potential function of intrinsic connectivity. These results provide analytic proof-of-principle for the existence of semi-stable states of cortical dynamics at the scale of a cortical column. Crucially, this work allows for model inversion of neural mass models, not only around fixed points, but over regions of phase space that encompass transitions among semi or multi-stable states of oscillatory activity. In principle, this formulation of cortical dynamics may improve our understanding of the itinerancy that underwrites measures of cortical activity (through EEG or MEG). Crucially, these theoretical results speak to model inversion in the context of multiple semi-stable brain states, such as onset of seizure activity in epilepsy or beta bursts in Parkinsons disease.

q-bio.NC↗

arXiv2022

Hints of the Quantum Nature of the Universe in Classical Electrodynamics and Their Connection to the Electronic Charge and Dark Energy

The electromagnetic fields of linear radiating systems working without dispersive and dissipative losses are analyzed both in the time and the frequency domains. In the case of the time domain radiating system, the parameter studied is the action, A, associated with the radiation. The action is defined as the product of the energy and the duration of the radiation. In the case of the frequency domain radiating system, which produces radiation in bursts of duration T/2 where T is the period of oscillation, the parameter studied is the energy, U, dissipated in a single burst of radiation of duration T/2. In this paper, we have studied how A and U vary as a function of the charge associated with the current in the radiating system and the ratio of the length of the radiating system and its radius. We have observed remarkable results when this ratio is equal to the ratio of the radius of the universe to the Bohr radius. In the case of the time domain radiating system, we have observed that when the charge associated with the current propagating along the radiator reaches the electronic charge, the action associated with the radiation reduces to h/2*pi where h is the Planck constant. In the case of the frequency domain radiating system, we have observed that as the magnitude of the oscillating charge reduces to the electronic charge, the energy dissipated in a single burst of radiation reduces to h*v, where v is the frequency of oscillation. Interestingly, all these results are based purely on classical electrodynamics and general relativity. The importance of the findings is discussed. In particular, the fact that the minimum free charge that exists in nature is the electronic charge, is shown for the first time to be a direct consequence of the photonic nature of the electromagnetic fields. Furthermore, the presented findings allow to derive for the first time an expression for the dark energy density of the universe in terms of the other fundamental constants in nature, the prediction of which is consistent with experimental observations. This Equation, which combines together the dark energy, electronic charge and mass, speed of light, gravitational constant and Planck constant, creates a link between classical field theories (i.e., classical electrodynamics and general relativity) and quantum mechanics.

physics.class-ph↗

arXiv2021

Could macroscopic dark matter (macros) give rise to mini-lightning flashes out of a blue sky without clouds?

A recent study pointed out that macroscopic dark matter (macros) traversing through the earth's atmosphere can give rise to hot and ionized channels similar to those associated with lightning leaders. The authors of the study investigated the possibility that when such channels created by macros pass through a thundercloud, lightning leaders may locked into these ionized channels creating lightning discharges with perfectly straight channels. They suggested the possibility of detecting such channels as a means of detecting the passage of macros through the atmosphere. In this paper, we show that macros crossing the atmosphere under fair weather conditions could also give rise to mini lightning flashes with current amplitudes in the order of few hundreds of Amperes. These mini lightning flashes would generate a thunder signature similar to or stronger than those of long laboratory sparks and they could also be detected by optical means. As in the case of thunderstorm assisted macro lightning, these mini-lightning flashes are also associated with straight channels. Moreover, since the frequency of mini lightning flashes are about three hundred times more frequent than the macro generated lightning flashes which were assisted by thunderstorms, they could be used as a means to look for the paths of macroscopic dark matter crossing the atmosphere.

physics.ao-ph↗