DSpace Community: KAIST College of Natural Sciences
http://hdl.handle.net/10203/11
KAIST College of Natural Sciences2020-07-08T02:42:51Zl-adic étale cohomology of Shimura varieties of Hodge type with non-trivial coefficients
http://hdl.handle.net/10203/251897
Title: l-adic étale cohomology of Shimura varieties of Hodge type with non-trivial coefficients
Authors: Hamacher, Paul; Kim, WansuChemotactic traveling waves with compact support
http://hdl.handle.net/10203/274129
Title: Chemotactic traveling waves with compact support
Authors: Choi, Sun-Ho; Kim, Yong-Jung
Abstract: A logarithmic model type chemotaxis equation is introduced with porous medium diffusion and a population dependent consumption rate. The classical assumption that individual bacterium can sense the chemical gradient is not taken. Instead, the chemotactic term appears by assuming that the migration distance is inversely proportional to the amount of food if food is the reason for migration. The existence and uniqueness of a traveling wave solution of the model are obtained. In particular, solutions have interfaces that divide into constant and non-constant regions. In particular, the profile of the population distribution has compact support. Numerical simulations are provided and compared with analytic results.2020-08-01T00:00:00ZOn an optimal quadrature formula for approximation of Fourier integrals in the space L-2((1))
http://hdl.handle.net/10203/273507
Title: On an optimal quadrature formula for approximation of Fourier integrals in the space L-2((1))
Authors: Hayotov, Abdullo R.; Jeon, Soomin; Lee, Chang-Ock
Abstract: This paper deals with the construction of an optimal quadrature formula for approximation of Fourier integrals in the Sobolev space L-2((1)) [a, b] of non-periodic, complex valued functions which are square integrable with first order derivative. Here the quadrature sum consists of linear combination of the given function values in a uniform grid. The difference between the integral and the quadrature sum is estimated by the norm of the error functional. The optimal quadrature formula is obtained by minimizing the norm of the error functional with respect to coefficients. Analytic formulas for optimal coefficients can also be obtained using discrete analogue of the differential operator d(2)/dx(2). In addition, the convergence order of the optimal quadrature formula is studied. It is proved that the obtained formula is exact for all linear polynomials. Thus, it is shown that the convergence order of the optimal quadrature formula for functions of the space C-2[a, b] is O(h(2)). Moreover, several numerical resudlts are presented and the obtained optimal quadrature formula is applied to reconstruct the X-ray Computed Tomography image by approximating Fourier transforms.2020-07-01T00:00:00ZGrowth of a-axial GaN core nanowires, semi-polar (1(1)over-bar01) GaN/InGaN multiple quantum well co-axial nanowires on Si substrate, and their carrier dynamics
http://hdl.handle.net/10203/275134
Title: Growth of a-axial GaN core nanowires, semi-polar (1(1)over-bar01) GaN/InGaN multiple quantum well co-axial nanowires on Si substrate, and their carrier dynamics
Authors: Johar, Muhammad Ali; Waseem, Aadil; Song, Hyun-Gyu; Hassan, Mostafa Afifi; Bagal, Indrajit V.; Cho, Yong-Hoon; Ryu, Sang-Wan
Abstract: The quantum-confined Stark effect (QCSE) reduces the quantum efficiency of optical devices due to the reduced overlap of electron and hole wave functions because of the growth of GaN/InGaN multiple quantum wells (MQWs) on the polar facet. Here, we report the growth of non-polar [1 (1) over bar 20] GaN core nanowires on Si substrate by MOCVD. Subsequently, the active region of GaN/InGaN MQWs is grown on (1 (1) over bar 01) semipolar growth facet. The morphology of GaN core and GaN/InGaN MQWs is examined by SEM and TEM. The growth direction of GaN core and GaN/InGaN MQWs is confirmed by SAED patterns. The bandgap is tuned from 3.11 eV to 2.45 eV by increasing the InGaN QW thickness. Finally, time-resolved photoluminescence is conducted to evaluate the carrier dynamics. An ultrashort time constant between 51 ps and 74 ps is measured with increased QW thickness. The underlying reason for the very short carrier lifetime is the suppressed QCSE because the piezoelectric and polarization fields are reduced due to the semi-polar growth facet of QWs. The semi-polar growth of GaN/InGaN MQW co-axial nanowires on Si substrate underlines the potential of our fabrication technique for a variety of optical applications.2020-07-01T00:00:00Z