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Search Results: 1 - 7 of 7 matches for " Thaned Rojsiraphisal "
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The Use of MTM-SVD Technique to Explore the Joint Spatiotemporal Modes of Wind and Sea Surface Variability in the North Indian Ocean during 1993–2005
Thaned Rojsiraphisal,Balaji Rajagopalan,Lakshmi Kantha
International Journal of Oceanography , 2009, DOI: 10.1155/2009/214828
Abstract: Sea surface height (SSH) and sea surface temperature (SST) in the North Indian Ocean are affected predominantly by the seasonally reversing monsoons and in turn feed back on monsoon variability. In this study, a set of data generated from a data-assimilative ocean model is used to examine coherent spatiotemporal modes of variability of winds and surface parameters using a frequency domain technique, Multiple Taper Method with Singular Value Decomposition (MTM-SVD). The analysis shows significant variability at annual and semiannual frequencies in these fields individually and jointly. The joint variability of winds and SSH is significant at interannual (2-3 years) timescale related to the ENSO mode—with a “/dipole/” like spatial pattern. Joint variability with SST showed similar but somewhat weaker behavior. Winds appear to be the driver of variability in both SSH and SST at these frequency bands. This offers prospects for long-lead projections of the North Indian Ocean climate.
Compact FPGA-based pulse-sequencer and radio-frequency generator for experiments with trapped atoms
Thaned Pruttivarasin,Hidetoshi Katori
Physics , 2015, DOI: 10.1063/1.4935476
Abstract: We present a compact FPGA-based pulse sequencer and radio-frequency (RF) generator suitable for experiments with cold trapped ions and atoms. The unit is capable of outputting a pulse sequence with at least 32 TTL channels with a timing resolution of 40 ns and contains a built-in 100 MHz frequency counter for counting electrical pulses from a photo-multiplier tube (PMT). There are 16 independent direct-digital-synthesizers (DDS) RF sources with fast (rise-time of ~60 ns) amplitude switching and sub-mHz frequency tuning from 0 to 800 MHz.
Energy Transport in Trapped Ion Chains
Michael Ramm,Thaned Pruttivarasin,Hartmut H?ffner
Physics , 2013, DOI: 10.1088/1367-2630/16/6/063062
Abstract: We experimentally study energy transport in chains of trapped ions. We use a pulsed excitation scheme to rapidly add energy to the local motional mode of one of the ions in the chain. Subsequent energy readout allows us to determine how the excitation has propagated throughout the chain. We observe energy revivals that persist for many cycles. We study the behavior with an increasing number of ions of up to 37 in the chain, including a zig-zag configuration. The experimental results agree well with the theory of normal mode evolution. The described system provides an experimental toolbox for the study of thermodynamics of closed systems and energy transport in both classical and quantum regimes.
Direct spectroscopy of the $^2$S$_{1/2}-^2$P$_{1/2}$ and $^2$D$_{3/2}-^2$P$_{1/2}$ transitions and observation of micromotion modulated spectra in trapped \Ca
Thaned Pruttivarasin,Michael Ramm,Hartmut Haeffner
Physics , 2013, DOI: 10.1088/0953-4075/47/13/135002
Abstract: We present an experimental scheme to perform spectroscopy of the $^2$S$_{1/2}-^2$P$_{1/2}$ and $^2$D$_{3/2}-^2$P$_{1/2}$ transitions in \Ca. By rapidly switching lasers between both transitions, we circumvent the complications of both dark resonances and Doppler heating. We apply this method to directly observe the micromotion modulated fluorescence spectra of both transitions and measure the dependence of the micromotion modulation index on the trap frequency. With a measurement time of 10 minutes, we can detect the center frequencies of both dipole transitions with a precision on the order of 200 kHz even in the presence of strong micromotion.
Delay-Dependent Guaranteed Cost Controller Design for Uncertain Neural Networks with Interval Time-Varying Delay
M. Rajchakit,P. Niamsup,T. Rojsiraphisal,G. Rajchakit
Abstract and Applied Analysis , 2012, DOI: 10.1155/2012/587426
Abstract: This paper studies the problem of guaranteed cost control for a class of uncertaindelayed neural networks. The time delay is a continuous function belonging to a giveninterval but not necessary to be differentiable. A cost function is considered as anonlinear performance measure for the closed-loop system. The stabilizing controllersto be designed must satisfy some exponential stability constraints on the closed-looppoles. By constructing a set of augmented Lyapunov-Krasovskii functionals combinedwith Newton-Leibniz formula, a guaranteed cost controller is designed via memorylessstate feedback control, and new sufficient conditions for the existence of the guaranteedcost state feedback for the system are given in terms of linear matrix inequalities(LMIs). Numerical examples are given to illustrate the effectiveness of the obtainedresult.
North Indian Ocean variability during the Indian Ocean dipole
J. Brown,C. A. Clayson,L. Kantha,T. Rojsiraphisal
Ocean Science Discussions (OSD) , 2008,
Abstract: The circulation in the North Indian Ocean (NIO henceforth) is highly seasonally variable. Periodically reversing monsoon winds (southwesterly during summer and northeasterly during winter) give rise to seasonally reversing current systems off the coast of Somalia and India. In addition to this annual monsoon cycle, the NIO circulation varies semiannually because of equatorial currents reversing four times each year. These descriptions are typical, but how does the NIO circulation behave during anomalous years, during an Indian Ocean dipole (IOD) for instance? Unfortunately, in situ observational data are rather sparse and reliance has to be placed on numerical models to understand this variability. In this paper, we estimate the surface current variability from a 12-year hindcast of the NIO for 1993–2004 using a 1/2° resolution circulation model that assimilates both altimetric sea surface height anomalies and sea surface temperature. Presented in this paper is an examination of surface currents in the NIO basin during the IOD. During the non-IOD period of 2000–2004, the typical equatorial circulation of the NIO reverses four times each year and transports water across the basin preventing a large sea surface temperature difference between the western and eastern NIO. Conversely, IOD years are noted for strong easterly and westerly wind outbursts along the equator. The impact of these outbursts on the NIO circulation is to reverse the direction of the currents – when compared to non-IOD years – during the summer for negative IOD events (1996 and 1998) and during the fall for positive IOD events (1994 and 1997). This reversal of current direction leads to large temperature differences between the western and eastern NIO.
Precision Measurement Method for Branching Fractions of Excited P1/2 States Applied to 40Ca+
Michael Ramm,Thaned Pruttivarasin,Mark Kokish,Ishan Talukdar,Hartmut H?ffner
Physics , 2013, DOI: 10.1103/PhysRevLett.111.023004
Abstract: We present a method for measuring branching fractions for the decay of $J = 1/2$ atomic energy levels to lower-lying states based on time-resolved recording of the atom's fluorescence during a series of population transfers. We apply this method to measure the branching fractions for the decay of the 4$^{2}$P$_{1/2}$ state of $^{40}$\Ca to the 4$^{2}$S$_{1/2}$ and 3$^{2}$D$_{3/2}$ states to be \branching\ and \branchingsm, respectively. The measurement scheme requires that at least one of the lower-lying states be long-lived. The method is insensitive to fluctuations in laser light intensity and magnetic field and is readily applicable to various atomic species due to its simplicity. Our result distinguishes well among existing state-of-the-art theoretical models of \Ca.
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