Browsing by Author "Withoon Chunwachirasiri"

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    2D direct current resistivity modeling and inversion with hybrid FD-FE technique and 3D controlled-source electromagnetic modeling and inversion with scattered-field technique
    (Mahidol University. Mahidol University Library and Knowledge Center, 2013) Chatchai Vachiratienchai; Weerachai Siripunvaraporn; Phichet Kittara; Withoon Chunwachirasiri
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    Adsorption of metal-phthalocyanine molecule on aluminum (100) surface: The DFT study
    (2018-01-01) Asanee Somdee; Malliga Suewattana; Withoon Chunwachirasiri; Tanakorn Osotchan; Asawin Sinsarp; King Mongkut's University of Technology North Bangkok; Mahidol University
    © 2018 Thammasat University. All rights reserved. Adsorption of various metal-phthalocyanine (MPc) molecules on Al(100) substrate were investigated by using the Density functional Theory (DFT). There are six transition metal atoms substituted in phthalocyanine skeleton ranking from d 5 to d 10 of the 1 st row of transition metal and metal free phthalocyanine (H 2 Pc) molecule were studied. After adsorption, we found that the interaction between MPc molecules and substrate depended on the central metal of MPc molecule. The interaction between the ZnPc, CuPc and NiPc molecules on Al substrate are relatively weak comparing to the adsorption of H 2 Pc molecule, while the CoPc, FePc, and MnPc adsorptions show stronger interaction. This work are further investigated the vacuum level shift by extracting the information from the density of state (DOS) calculation. The shift of DOS of MPc molecule effect to the charge barriers at the interface.
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    Crustal structure study in Kanchanaburi province, Thailand using integrated geophysical methods
    (Mahidol University. Mahidol University Library and Knowledge Center, 2023) Songkhun Boonchaisuk; Weerachai Siripunvaraporn; Phichet Kittara; Withoon Chunwachirasiri
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    Description of states of two-photon interference in optical gating Michelson interferometer
    (2015-01-01) Ekkarat Pongophas; Asawin Sinsarp; Sujin Suwanna; Withoon Chunwachirasiri; Wisit Singhsomroje; Mahidol University
    © 2015 SPIE. The interference of two photons in the optical gating Michelson interferometer is investigated. The phenomenon is studied using two different representations of photons: the space-time domain and a step-by-step two photon state evolution. Both representations lead to an equivalent description of the two-photon states which is the interference of four cases of two-photon traveling states, as implied by the evolution analysis. Additionally, the space-time domain analysis reveals that the classical interference of high-intensity light source is identical to the two-photon interference in the quantum regime except for a multiplicative factor of (n2), where n is the number of photons.
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    Description of the states of two-photon interference in an optical gating Michelson interferometer
    (2016-01-01) Ekkarat Pongophas; Watthana Sriklin; Asawin Sinsarp; Sujin Suwanna; Withoon Chunwachirasiri; Wisit Singhsomroje; Mahidol University
    © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE). We investigate the interference of two photons in an optical gating Michelson interferometer. The phenomenon is studied using two different representations of photons: the space-time domain and a step-by-step two-photon state evolution. Both representations lead to identical results. The evolution analysis describes the result by the interference of four two-photon traveling states, whereas the space-time domain analysis reveals that the classical interference of the high-intensity light source is identical to two-photon interference in the quantum regime, except for a multiplicative factor of (n2), where n is the number of photons.
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    Effect of skeleton conformation on the electronic structure of 50% Ti substituted polysilanes from density functional calculations
    (2015-01-01) Asanee Somdee; Malliga Suewattana; Asawin Sinsarp; Withoon Chunwachirasiri; Mahidol University
    © 2015 Elsevier B.V. All rights reserved. We study the effect of skeleton conformations on the electronic structure of polysilanes and polysilanes with 50% Ti substitution (polytitasilanes) using first principle calculations. Various conformations including a trans-planar and a helical geometry of the skeleton backbone are examined. We found that in all cases, as the skeleton backbone is twisted away from being trans-planar, the bandgap increases. The overall band structures also exhibit some differences between the planar and helical configurations. The density of states shows that as Ti atoms are incorporated into the silane systems, the frontier state narrows indicating that the Ti substitution plays a major role at the lowest unoccupied conduction band and the highest occupied valance band. In addition, the backbone conformation has a strong influence on the bandgap and the frontier state for polytitasilanes which is not as apparent in the polysilanes.
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    Generation of Polarization-Entangled Photons with linear optical devices and SPDC type I process
    (Mahidol University. Mahidol University Library and Knowledge Center, 2024) Watthana Sriklin; Wisit Singhsomroje; Withoon Chunwachirasiri; Asawin Sinsarp; Sujin Suwanna; Pruet Kalasuwan
    In this thesis, we studied the entangled state of the photons. Our work was separated into two parts. In the first part, we proposed a design of a linear optical circuit that did not rely on nonlinear optic crystals to generate entangled photon pairs from non-entangled photons with high probability. The circuit design employed the Michelson's interferometer to create photon entanglement in the polarization basis. It was shown that by calculation corresponding to each junction in the circuit and the post selection, the designed circuit could produce the desired entangled photon states. From calculation, we could provide the Bell's states |Ψ--> and |Φ--> from post-selection at the output of the circuit. In the second part, we set up an experiment to create the polarized entangled photon pairs. In this work, we employed the spontaneous parametric down-conversion (SPDC) type I process in the nonlinear crystal which was beta barium borate (BBO) to produce the Bell's state |Φ+>. After that, we measured the correlation value and compared it with CHSH Bell's inequality to confirm the quantum entanglement. The result of the correlation value was 2.387±0.035 which violated the CHSH Bell's inequality. Therefore, we were able to obtained the polarized entangled photon pairs.
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    Mapping active faults with seismic methods in Kanchanaburi province, western Thailand and cavity detection with a 2-D DC resistivity method in karst terrain at Mahidol University, Kanchanaburi campus
    (Mahidol University. Mahidol University Library and Knowledge Center, 2012) Ananya Satitpittakul; Weerachai Siripunvaraporn; Siriporn Chaisri; Withoon Chunwachirasiri
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    Price-profit and price-volume relationships in a financial market by agent-based models
    (Mahidol University. Mahidol University Library and Knowledge Center, 2023) Kittiwat Tangmongkollert; Sujin Suwanna; Asawin Sinsarp; Wisit Singhsomroje; Withoon Chunwachirasiri
    In this dissertation, we performed agent-based dynamics simulations to investigate the price-profit and price-volume relations in a financial market. For the priceprofit relationship, effects such as the herding behavior and external information normally occur in a financial market, which influence the asset price and the price-profit relation. We constructed two coupled ring networks consisting of agents or traders in each network. The agents' decisions to buy or sell the asset follow the two-state Ising model dynamics, where the Metropolis algorithm was employed to determine the equilibrium state. Based on the principle of demand and supply, the price and profit profiles were modeled and calculated from the Ising magnetization. The obtained results suggested that traders should follow the majority of agents in order to get maximum profits, and the disagreement between agents in a market never benefit any traders. For the price and trading volume relations in a stock market, we similarly used an agent-based model, and implemented a decision-making algorithm based on the order book trading. We assumed that the agents represent the so-called "value investors" in the system. An agent would likely buy a stock if its current price is lower than the pseudo fundamental price, and likely sell if vice versa. The simulation results show that the trading volume became significantly high whenever there is a big change in the asset price. More importantly, it reveals asymmetry; namely, the trading volume became much higher in the selling phase than that in the buying phase. This suggests that traders could get a warning signal of a market crash from the trading volume. Such simple agent-based models can reveal important phenomena in a financial market which have been observed and verified empirically over years.
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    Two-dimensional joint inversion of direct-current resistivity data and magnetotelluric data
    (Mahidol University. Mahidol University Library and Knowledge Center, 2010) Puwis Amatyakul; Weerachai Siripunvaraporn; Phichet Kittara; Withoon Chunwachirasiri