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Min-Ho Lee

Publications and source records attributed to Min-Ho Lee.

15 recordsLinked to original sources
arXiv2020

A BCI based Smart Home System Combined with Event-related Potentials and Speech Imagery Task

Recently, smart home systems based on brain-computer interface (BCI) has attracted a wide range of interests in both industry and academia. However, the current BCI system has several shortcomings as it produces a comparatively lower accuracy for real-time implementations as well as the intuitive paradigm for the users cannot be well established here. Therefore, in this study, we proposed a highly intuitive BCI paradigm that combines event-related potential (ERP) with the speech-imagery task for the individual target objects. The decoding accuracy of the proposed paradigm was 88.1% (plus or minus 5.90) which is a much significant higher performance than a conventional ERP system. Furthermore, the amplitude of N700 components was significantly enhanced over frontal regions which are priory evoked by the speech-imagery task. Our results could be utilized to develop a smart home system so that it could be more user-friendly and convenient by means of delivering user's intentions both, intuitively and accurately.

cs.HC↗
arXiv2015

Classical Mechanics of Collinear Positron-Hydrogen Scattering

We study the classical dynamics of the collinear positron-hydrogen scattering system below the three-body breakup threshold. Observing the chaotic behavior of scattering time signals, we in- troduce a code system appropriate to a coarse grained description of the dynamics. And, for the purpose of systematic analysis of the phase space structure, a surface of section is introduced being chosen to match the code system. Partition of the surface of section leads us to a surprising conjec- ture that the topological structure of the phase space of the system is invariant under exchange of the dynamical variables of proton with those of positron. It is also found that there is a finite set of forbidden patterns of symbol sequences. And the shortest periodic orbit is found to be stable, around which invariant tori form an island of stability in the chaotic sea. Finally we discuss a possible quantum manifestation of the classical phase space structure relevant to resonances in scattering cross sections.

physics.atom-ph↗
arXiv2007

Evidence of triple collision dynamics in partial photo-ionisation cross sections of helium

Experimental results on partial photo-ionisation cross sections of helium are analysed in the light of recent advances in the semiclassical theory of two-electron atoms. Byun et al (arXiv:physics/0701086) predict that the total photo-ionisation cross section below the double-ionisation threshold can, semiclassically, be described in terms of contributions associated with classical orbits starting and ending in the triple collision. The necessary modifications of the semiclassical theory for partial cross sections is developed here. It is argued that partial cross sections are also dominated by the triple collision dynamics. The expected semiclassical contributions can be identified in the Fourier transformation of the experimental data. This clearly demonstrates for the first time the validity of the basic assumptions made in Byun et al. Our findings explain furthermore in a natural way the self-similar structures observed in cross section signals for different channel numbers.

physics.atom-ph↗
arXiv2007

Scaling laws for the photo-ionisation cross section of two-electron atoms

The cross sections for single-electron photo-ionisation in two-electron atoms show fluctuations which decrease in amplitude when approaching the double-ionisation threshold. Based on semiclassical closed orbit theory, we show that the algebraic decay of the fluctuations can be characterised in terms of a threshold law $σ\propto |E|^μ$ as $E \to 0_-$ with exponent $μ$ obtained as a combination of stability exponents of the triple-collision singularity. It differs from Wannier's exponent dominating double ionisation processes. The details of the fluctuations are linked to a set of infinitely unstable classical orbits starting and ending in the non-regularisable triple collision. The findings are compared with quantum calculations for a model system, namely collinear helium.

physics.atom-ph↗
arXiv2004

The classical dynamics of two-electron atoms near the triple collision

The classical dynamics of two electrons in the Coulomb potential of an attractive nucleus is chaotic in large parts of the high-dimensional phase space. Quantum spectra of two-electron atoms, however, exhibit structures which clearly hint at the existence of approximate symmetries in this system. In a recent paper,(Phys. Rev. Lett. 93, 054302 (2004)), we presented a study of the dynamics near the triple collision as a first step towards uncovering the hidden regularity in the classical dynamics of two electron atoms. The non-regularisable triple collision singularity is a main source of chaos in three body Coulomb problems. Here, we will give a more detailed account of our findings based on a study of the global structure of the stable and unstable manifolds of the triple collision.

nlin.CD↗
arXiv2004

Classical dynamics near the triple collision in a three-body Coulomb problem

We investigate the classical motion of three charged particles with both attractive and repulsive interaction.The triple collision is a main source of chaos in such three body Coulomb problems.By employing the McGehee scaling technique, we analyse here for the first time in detail the three-body dynamics near the triple collision in 3 degrees of freedom.We reveal surprisingly simple dynamical patterns in large parts of the chaotic phase space. The underlying degree of order in the form of approximate Markov partitions may help in understanding the global structures observed in quantum spectra of two-electron atoms.

nlin.CD↗
arXiv1997

Infinite Order Discrete Variable Representation for Quantum Scattering

A new approach to multi-dimensional quantum scattering by the infinite order discrete variable representation is presented. Determining the expansion coefficients of the wave function at the asymptotic regions by the solution of the differential Schrödinger equation, we reduce an infinite set of linear equations to a finite one. Application to the benchmark collinear $H + H_2 \to H_2 + H$ reaction is shown to yield precise reaction probabilities.

physics.atom-ph↗
arXiv1997

The origin of the area law of the entropy of a quantum field in a black hole

It is shown that that the area law for the entropy of a quantum field in the Schwarzschild black hole is due to the quantum statistics. The entropies for one particle, a Boltzmann gas, a quantum mechanical gas obeying Bose-Einstein or Fermi-Dirac statistics, and a quantum field in the Schwarzschild black hole are calculated using the microcanonical ensemble approach and the brick wall method. The area law holds only when the effect of quantum statistics is dominated.

gr-qc↗
arXiv1997

Exact wave functions and geometric phases of a generalized driven oscillator

The generalized invariant and its eigenstates of a general quadratic oscillator are found. The Schrödinger wave functions for the eigenstates are also found in analytically closed forms. The conditions for the existence of the cyclic initial state (CIS) are studied and the corresponding nonadiabatic Berry phase is calculated explicitly.

quant-ph↗
arXiv1996

The Entropy of the Complex Scalar Field in a Charged Kerr Black Hole

By using the brick wall method we calculate the thermodynamic potential of the complex scalar field in a charged Kerr black hole. Using it we show that in the Hartle-Hawking state the leading term of the entropy is proportional to $\frac{ A _H}{ε^2}$, which becomes divergent as the system approaches the black hole horizon. The origin of the divergence is that the density of states diverges at the horizon.

hep-th↗
arXiv1996

On the Entropy of a Quantum Field in the Rotating Black Holes

By using the brick wall method we calculate the free energy and the entropy of the scalar field in the rotating black holes. As one approaches the stationary limit surface rather than the event horizon in comoving frame, those become divergent. Only when the field is comoving with the black hole (i.e. $Ω_0 = Ω_H$) those become divergent at the event horizon. In the Hartle-Hawking state the leading terms of the entropy are $ A \frac{1}{h} + B \ln(h) + finite$, where $h$ is the cut-off in the radial coordnate near the horizon. In term of the proper distance cut-off $ε$ it is written as $ S = N A_H/ε^2$. The origin of the divergence is that the density of state on the stationary surface and beyond it diverges.

hep-th↗
arXiv1996

The Entropy of a Quantum Field in a Charged Kerr Black Hole

We calculate the entropies of the system of classical particles and a quantum scalar field by using the brick wall method in thermal bath in a charged Kerr black hole spacetime. Their leading terms at Hartle-Hawking temperature $T_H = κ/(2 π) $ are given by $ S_{cl} \approx N \ \ln \left( \frac{A_b}{ε^2} \right)$, and $S \approx N' \frac{A_H}{ε^2}$, where $A_b$ and $A_H$ are the area of the box and the horizon respectively.

hep-th↗
arXiv1993

Bose-Einstein condensation for a self-interacting theory in curved spacetime

The effective action is derived for a self-interacting theory with a finite fixed $O(2)$ charge at finite temperature in curved spacetime. We obtain the high temperature expansion of the effective action in the weak coupling limit. In the relativistic temperature, we discuss about the phase transition in a homogeneous spacetime.

hep-th↗