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Search Results: 1 - 10 of 551723 matches for " S. -J. Oh "
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Foregrounds for 21cm Observations of Neutral Gas at High Redshift
S. Peng Oh,Katherine J. Mack
Physics , 2003, DOI: 10.1111/j.1365-2966.2003.07133.x
Abstract: We investigate a number of potential foregrounds for an ambitious goal of future radio telescopes such as the Square Kilometer Array (SKA) and Low Frequency Array (LOFAR): spatial tomography of neutral gas at high redshift in 21cm emission. While the expected temperature fluctuations due to unresolved radio point sources is highly uncertain, we point out that free-free emission from the ionizing halos that reionized the universe should define a minimal bound. This emission is likely to swamp the expected brightness temperature fluctuations, making proposed detections of the angular patchwork of 21cm emission across the sky unlikely to be viable. An alternative approach is to discern the topology of reionization from spectral features due to 21cm emission along a pencil-beam slice. This requires tight control of the frequency-dependence of the beam in order to prevent foreground sources from contributing excessive variance. We also investigate potential contamination by galactic and extragalactic radio recombination lines (RRLs). These are unlikely to be show-stoppers, although little is known about the distribution of RRLs away from the Galactic plane. The mini-halo emission signal is always less than that of the IGM, making mini-halos unlikely to be detectable. If they are seen, it will be only in the very earliest stages of structure formation at high redshift, when the spin temperature of the IGM has not yet decoupled from the CMB.
Electroweak phase transitions in the MSSM with an extra $U(1)'$
Ham, S. W.;Yoo, E. J.;OH, S. K.
High Energy Physics - Phenomenology , 2007, DOI: 10.1103/PhysRevD.76.075011
Abstract: We investigate the possibility of electroweak phase transition in the minimal supersymmetric standard model (MSSM) with an extra $U(1)'$. This model has two Higgs doublets and a singlet, in addition to a singlet exotic quark superfield. We find that at the one-loop level this model may accommodate the electroweak phase transitions that are strongly first-order in a reasonably large region of the parameter space. In the parameter region where the phase transitions take place, we observe that the lightest scalar Higgs boson has a smaller mass when the strength of the phase transition becomes weaker. Also, the other three heavier neutral Higgs bosons get more large masses when the strength of the phase transition becomes weaker.
Explicit CP violation in a MSSM with an extra $U(1)'$
Ham, S. W.;Yoo, E. J.;OH, S. K.
High Energy Physics - Phenomenology , 2007, DOI: 10.1103/PhysRevD.76.015004
Abstract: We study that a minimal supersymmetric standard model with an extra $U(1)'$ gauge symmetry may accommodate the explicit CP violation at the one-loop level through radiative corrections. This model is CP conserving at the tree level and cannot realize the spontaneous CP violation for a wide parameter space at the one-loop level. In explicit CP violation scenario, we calculate the Higgs boson masses and the magnitude of the scalar-pseudoscalar mixings in this model at the one-loop level by taking into account the contributions of top quarks, bottom quarks, exotic quarks, and their superpartners. In particular, we investigate how the exotic quarks and squarks would affect the scalar-pseudoscalar mixings. It is observed that the size of the mixing between the heaviest scalar and pseudoscalar Higgs bosons is changed up to 20 % by a complex phase originated from the exotic quark sector of this model.
Electroweak phase transition in the MNMSSM with explicit CP violation
Ham, S. W.;Im, J. O.;OH, S. K.
High Energy Physics - Phenomenology , 2007,
Abstract: In explicit CP violation scenario of the minimal non-minimal supersymmetric standard model (MNMSSM), the possibility of a strongly first-order electroweak phase transition (EWPT) is investigated at the one-loop level, where the radiative corrections from the loops of the top and stop quarks are taken into account. Assuming that the stop quark masses are not degenerate, the radiative corrections due to the stop quarks give rise to a CP phase, which triggers the scalar-pseudoscalar mixing in the Higgs sector of the MNMSSM. The lighter stop quark need not always to have a small mass in order to ensure the strongly first-order EWPT. In the MNMSSM with explicit CP violation, it is found that the strength of the first-order EWPT depends on several factors, such as the lightest neutral Higgs boson mass and the nontrivial CP phase arising from stop quark masses. The effects of these factors are discussed.
Charged Higgs boson in the next-to-minimal supersymmetric standard model with explicit CP violation
S. W. Ham,J. Kim,S. K. Oh,D. Son
Physics , 2001, DOI: 10.1103/PhysRevD.64.035007
Abstract: The phenomenology of the explicit CP violation in the Higgs sector of the next-to-minimal supersymmetric standard model (NMSSM) is investigated, with emphasis on the charged Higgs boson. The radiative corrections due to both quarks and scalar-quarks of the third generation are taken into account, and the negative result of the search for the Higgs bosons at CERN LEP2, with the discovery limit of 0.1 pb, is imposed as a constraint. It is found that there are parameter regions of the NMSSM where the lightest neutral Higgs boson may even be massless, without being detected at LEP2. This implies that the LEP2 data do not contradict the existence of a massless neutral Higgs boson in the NMSSM. For the charged Higgs boson, the radiative corrections to its mass may be negative in some parameter regions of the NMSSM. The phenomenological lower bound on the radiatively corrected mass of the charged Higgs boson is increased as the CP violation becomes maximal, i.e., as the CP violating phase becomes $\pi/2$. At the maximal CP violation, its lower bound is about 110 GeV for 5 $\leqslant \tan \beta \leqslant$ 40. The vacuum expectation value (VEV) of the neutral Higgs singlet is shown to be no smaller than 16 GeV for any parameter values of the NMSSM with explicit CP violation. This value of the lower limit is found to increase up to about 45 GeV as the ratio ($\tan \beta$) of the VEVs of the two Higgs doublets decreases to smaller values ($\sim$ 2). The discovery limit of the Higgs boson search at LEP2 is found to cover about a half of the kinematically allowed part of the whole parameter space of the NMSSM, and the portion is roughly stable against the CP violating phase.
Genetic Algorithm-based Dynamic Vehicle Route Search using Car-to-Car Communication
Advances in Electrical and Computer Engineering , 2010, DOI: 10.4316/aece.2010.04013
Abstract: Suggesting more efficient driving routes generate benefits not only for individuals by saving commute time, but also for society as a whole by reducing accident rates and social costs by lessening traffic congestion. In this paper, we suggest a new route search algorithm based on a genetic algorithm which is more easily installable into mutually communicating car navigation systems, and validate its usefulness through experiments reflecting real-world situations. The proposed algorithm is capable of searching alternative routes dynamically in unexpected events of system malfunctioning or traffic slow-downs due to accidents. Experimental results demonstrate that our algorithm searches the best route more efficiently and evolves with universal adaptability.
Neuromuscular effects of G93A-SOD1 expression in zebrafish
Sakowski Stacey A,Lunn J,Busta Angela S,Oh Sang
Molecular Neurodegeneration , 2012, DOI: 10.1186/1750-1326-7-44
Abstract: Background Amyotrophic lateral sclerosis (ALS) is a fatal disorder involving the degeneration and loss of motor neurons. The mechanisms of motor neuron loss in ALS are unknown and there are no effective treatments. Defects in the distal axon and at the neuromuscular junction are early events in the disease course, and zebrafish provide a promising in vivo system to examine cellular mechanisms and treatments for these events in ALS pathogenesis. Results We demonstrate that transient genetic manipulation of zebrafish to express G93A-SOD1, a mutation associated with familial ALS, results in early defects in motor neuron outgrowth and axonal branching. This is consistent with previous reports on motor neuron axonal defects associated with familial ALS genes following knockdown or mutant protein overexpression. We also demonstrate that upregulation of growth factor signaling is capable of rescuing these early defects, validating the potential of the model for therapeutic discovery. We generated stable transgenic zebrafish lines expressing G93A-SOD1 to further characterize the consequences of G93A-SOD1 expression on neuromuscular pathology and disease progression. Behavioral monitoring reveals evidence of motor dysfunction and decreased activity in transgenic ALS zebrafish. Examination of neuromuscular and neuronal pathology throughout the disease course reveals a loss of neuromuscular junctions and alterations in motor neuron innervations patterns with disease progression. Finally, motor neuron cell loss is evident later in the disease. Conclusions This sequence of events reflects the stepwise mechanisms of degeneration in ALS, and provides a novel model for mechanistic discovery and therapeutic development for neuromuscular degeneration in ALS.
Characterising the ductility and fatigue crack resistance potential of asphalt mixes based on the laboratory direct tensile strength test
L F Walubita,G S Simate,J H Oh
Journal of the South African Institution of Civil Engineering , 2010,
Abstract: As a means to investigate the applicability of the direct tensile strength (DT) test as a surrogate fatigue crack test, the ductility and fatigue crack resistance potential of various asphalt (HMA) mixes were evaluated in the laboratory using the DT test, at ambient temperature (20oC) and a displacement loading rate of 1,27 mm/min. Various HMA mixes were included in the DT test program and the results were compared with those of the Overlay Tester, also conducted at ambient temperature. Up to 23 commonly used Texas HMA mixes with different mix design characteristics were evaluated and are discussed in this paper. The results indicated that the mix design volumetrics, such as the asphalt binder content and aggregate gradation, play a significant role in the ductility and fatigue crack resistance potential of HMA mixes. The dense-to fine-graded HMA mixes with high asphalt binder content exhibited better ductility potential and laboratory fatigue crack resistance than the coarse- and open-graded mixes. Overall, the DT test was found to be a promising surrogate fatigue crack test for mix design and HMA mix screening for fatigue crack resistance in the laboratory. Recommendations to improve the test protocol are included in the paper. However, sample fabrication and test set-up were the two critical issues found to be associated with the DT test.
On the sign of the pi-rho-omega coupling constant
K. Nakayama,Yongseok Oh,J. Haidenbauer,T. -S. H. Lee
Physics , 2006, DOI: 10.1016/j.physletb.2007.03.034
Abstract: It is shown that the relative sign between the $NN\omega$ and $\pi\rho\omega$ coupling constants can be determined most sensitively from $\omega$ production processes in $NN$ collisions. Recent data on these reactions clearly favor the sign of the $\pi\rho\omega$ coupling constant which is opposite to that inferred from studies of the photoproduction reaction in combination with the vector meson dominance assumption and used by many authors. Implication of this finding in the description of other reactions is discussed.
Higher dimensional cosmological model with a phantom field
S. T. Hong,J. Lee,T. H. Lee,P. OH
Physics , 2008, DOI: 10.1103/PhysRevD.78.047503
Abstract: We consider a higher dimensional gravity theory with a negative kinetic energy scalar field and a cosmological constant. We find that the theory admits an exact cosmological solution for the scale factor of our universe. It has the feature that the universe undergoes a continuous transition from deceleration to acceleration at some finite time. This transition time can be interpreted as that of recent acceleration of our universe.
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