1,721,968 research outputs found
Fast peak quench of the exciton transition in extremely shallow quantum well structures
No full textThe radius and binding energy of exciton in an extremely shallow quantum well (ESQW) structure are calculated theoretically. As the strength of applied electric field increases, the exciton radius increases and the binding energy decreases rapidly compared with a conventional quantum well, which explains the rapid peak quench in ESQW structures.X11sci
The exciton transition in extremely shallow quantum well structures: Strong coupling between the distributions in the quantized and in-plane directions
No full textThe planar radius and the binding energy of excitons in extremely shallow quantum well (ESQW) structures are calculated theoretically. As the strength of an applied electric field increases, the exciton planar radius increases and the binding energy decreases rapidly compared with a conventional quantum well, which explains the rapid peak quench in ESQW structures. We also calculate the energy difference between heavy hole and light hole exciton transitions in quantum wells with various barrier heights. Due to the small energy difference in ESQW structures, the light hole peak is not clearly resolved from heavy hole peak by room-temperature photocurrent experiments. (C) 1996 American Institute of Physics.open114sciescopu
Erdos-Posa property of chordless cycles and its applications
No full textA chordless cycle, or equivalently a hole, in a graph G is an induced subgraph of G which is a cycle of length at least 4. We prove that the Erdos-Posa property holds for chordless cycles, which resolves the major open question concerning the Erdos-Posa property. Our proof for chordless cycles is constructive: in polynomial time, one can find either k + 1 vertex-disjoint chordless cycles, or c(1)k(2) log k + c(2) vertices hitting every chordless cycle for some constants c(1) and c(2). It immediately implies an approximation algorithm of factor 0(opt log opt) for CHORDAL VERTEX DELETION. We complement our main result by showing that chordless cycles of length at least P for any fixed l >= 5 do not have the Erdos-Posa property. (C) 2020 The Authors. Published by Elsevier Inc.
On the Erdős-Pósa property for long holes in C_4-free graphs
No full textWe prove that there exists a function f(k)=O(k^2logk) such that for every C4-free graph G and every k∈N, G either contains k vertex-disjoint holes of length at least 6, or a set X of at most f(k) vertices such that G−X has no hole of length at least 6. This answers a question of Kim and Kwon [Erdős-Pósa property of chordless cycles and its applications. JCTB 2020
Optical encoder based on rectangular photonic quantum ring laser's orthogonal polarisation states
No full textA new type of optical encoder based on linearly polarised light from a photonic quantum ring (PQR) laser is reported. An encoded track of alternating p(1)- and p(2)-orthogonally polarised emission states embedded in a zigzag-shaped PQR laser train is read with a polarised photodetector in order to realise a polarisation-resolved positional detection scheme.X1122sciescopu
Dielectric constant anisotropy in glass phase of mixed crystal
No full text학위논문(석사) - 한국과학기술원 : 물리학과, 1990.2, [ [ii], 35 p. ]한국과학기술원 : 물리학과
The metastability of n-type a-Si:H depending on deposition temperature and rapid cooling
No full text학위논문(석사) - 한국과학기술원 : 물리학과, 1995.2, [ 37 p. ]한국과학기술원 : 물리학과
Spontaneous bursting of hodgkin-huxley neurons in small-world network
No full text학위논문(석사) - 한국과학기술원 : 물리학과, 2001.2, [ [ii], 44 p. ]한국과학기술원 : 물리학과
잡음에 노출된 비국소적으로 연결된 흥분 세포들의 컴퓨터 시늉을 이용한 연구
No full text학위논문(박사) - 한국과학기술원 : 물리학과, 2006.2, [ ix, 59 p. ]The response of nonlinear systems to noise is very interesting research topic. Especially, stochastic resonance (SR) has attracted large attention during the last two decades. The basic result of SR shows that the response of a nonlinear system is optimized at a certain finite level, neither very weak nor very strong, of noise. Here, optimized response means that a system detects very weak signal aid by optimal noise and can show most coherent motion aid by optimal noise. The SR phenomena have emerged in many fields, from physical to biological systems. In particular, SR has been studied very extensively due to an application in information process of neuroscience.
In this thesis, we investigate the response of neural network to noise for two neuron models with numerical method. Previous studies have been conducted on regular or fully random network mainly. But it is well known that biological neural network present a clear clustering in their neurons but have small distances between each pair of neurons. This kind of network is known as small-world network. Therefore, throughout this work, we employ Watts-Strogatz small-world network as a connection topology.
Firstly, we investigate the coherence resonance (CR) of Hodgkin-Huxley neurons. It is found that increasing the randomness p of the network topology leads to an enhancement of temporal coherence and of spatial synchronization. Especially, it is found that (1) spatial synchronization increase as characteristic path length L shortens and (2) firing frequency increases as clustering coefficient C decreases. We introduce constant-clustering network. In such a network, synchronization increases as L shortens, but firing frequency remains constantly. This result leads to more confidence of above relations.
Secondly, we study the effect of spatially correlated noise on CR in neural network of Fitz Hugh-Nagumo neurons, where the noise correlation decays exponentially with distance between neurons. For intermediat...한국과학기술원 : 물리학과
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