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T. Kim

Publications and source records attributed to T. Kim.

At least 55 records · Page 3Linked to original sources
arXiv2014

Initial Results of a Silicon Sensor Irradiation Study for ILC Extreme Forward Calorimetry

Detectors proposed for the International Linear Collider (ILC) incorporate a tungsten sampling calorimeter (`BeamCal') intended to reconstruct showers of electrons, positrons and photons that emerge from the interaction point of the collider with angles between 5 and 50 milliradians. For the innermost radius of this calorimeter, radiation doses at shower-max are expected to reach 100 MRad per year, primarily due to minimum-ionizing electrons and positrons that arise in the induced electromagnetic showers of e+e- `beamstrahlung' pairs produced in the ILC beam-beam interaction. However, radiation damage to calorimeter sensors may be dominated by hadrons induced by nuclear interactions of shower photons, which are much more likely to contribute to the non-ionizing energy loss that has been observed to damage sensors exposed to hadronic radiation. We report here on the results of SLAC Experiment T-506, for which several different types of silicon diode sensors were exposed to doses of radiation induced by showering electrons of energy 3.5-10.6 GeV. By embedding the sensor under irradiation within a tungsten radiator, the exposure incorporated hadronic species that would potentially contribute to the degradation of a sensor mounted in a precision sampling calorimeter. Depending on sensor technology, efficient charge collection was observed for doses as large as 220 MRad.

physics.ins-det↗
arXiv2013

A quasi-solution approach to nonlinear problems - the case of Blasius similarity solution

Using the simple case of Blasius similarity solution, we illustrate a recently developed general method that reduces a strongly nonlinear problem into a weakly nonlinear analysis. The basic idea is to find a quasi-solution $F_0$ that satisfies the nonlinear problem and boundary conditions to within small errors. Then, by decomposing the true solution $F=F_0+E$, a weakly nonlinear analysis of $E$, using contraction mapping theorem in a suitable space of functions provides the existence of solution as well as bounds on the error $E$. The quasi-solution construction relies on a combination of exponential asymptotics and standard orthogonal polynomial representations in finite domain.

math.CA↗
arXiv2013

Morphological Parameters of Spitzer Survey of Stellar Structure in Galaxies (S4G)

The morphology of galaxies can be quantified to some degree using a set of scale-invariant parameters. Concentration (C), Asymmetry (A), Smoothness (S), the Gini index (G), relative contribution of the brightest pixels to the second order moment of the flux (M20), ellipticity (E), and the Gini index of the second order moment (GM) have all been applied to morphologically classify galaxies at various wavelengths. Here we present a catalog of these parameters for the Spitzer Survey of Stellar Structure in Galaxies (S4G), a volume-limited near-infrared imaging survey of nearby galaxies using the 3.6 and 4.5 micron channels of the IRAC camera. Our goal is to provide a reference catalog of near-infrared quantified morphology for high-redshift studies and galaxy evolution models with enough detail to resolve stellar mass morphology. We explore where normal, non-interacting galaxies -those typically found on the Hubble tuning fork- lie in this parameter space and show that there is a tight relation between Concentration and M20 for normal galaxies. M20 can be used to classify galaxies into earlier and later types (e.g., to separate spirals from irregulars). Several criteria using these parameters exist to select systems with a disturbed morphology, i.e., those that appear to be undergoing a tidal interaction. We examine the applicability of these criteria to Spitzer near-infrared imaging. We find that four relations, based on the parameters A&S, G&M20, GM, and C&M20, respectively, select outliers in the morphological parameter space, but each selects different subsets of galaxies. Two criteria (GM > 0.6, G > -0.115 x M20 + 0.384) seem most appropriate to identify possible mergers and the merger fraction in near-infrared surveys. We find no strong relation between lopsidedness and most of these morphological parameters, except for a weak dependence of lopsidedness on Concentration and M20.

astro-ph.CO↗
arXiv2013

The impact of bars on disk breaks as probed by S4G imaging

We have analyzed the radial distribution of old stars in a sample of 218 nearby face-on disks, using deep 3.6um images from the Spitzer Survey of Stellar Structure in Galaxies (S4G). In particular, we have studied the structural properties of those disks with a broken or down-bending profile. We find that, on average, disks with a genuine single exponential profile have a scale-length and a central surface brightness which are intermediate to those of the inner and outer components of a down-bending disk with the same total stellar mass. In the case of barred galaxies, the ratio between the break and the bar radii (Rbr/Rbar) depends strongly on the total stellar mass of the galaxy. For galaxies more massive than 10^10 Msun, the distribution is bimodal, peaking at Rbr/Rbar~2 and ~3.5. The first peak, which is the most populated one, is linked to the Outer Lindblad Resonance of the bar, whereas the second one is consistent with a dynamical coupling between the bar and the spiral pattern. For galaxies below 10^10 Msun, breaks are found up to ~10 Rbar, but we show that they could still be caused by resonances given the rising nature of rotation curves in these low-mass disks. While not ruling out star formation thresholds, our results imply that radial stellar migration induced by non-axysymmetric features can be responsible not only for those breaks at 2 Rbar, but also for many of those found at larger radii.

astro-ph.CO↗
arXiv2013

On the associated sequences of special polynomials

In this paper, we investigate some properties of the associated sequence of Daehee and Changhee polynomials. Finally, we give some interesting identities of associated sequence involving some special polynomials.

math.NT↗
arXiv2012

Filon-Clenshaw-Curtis rules for highly-oscillatory integrals with algebraic singularities and stationary points

In this paper we propose and analyse composite Filon-Clenshaw-Curtis quadrature rules for integrals of the form $I_{k}^{[a,b]}(f,g) := \int_a^b f(x) \exp(\mathrm{i}kg(x)) \rd x $, where $k \geq 0$, $f$ may have integrable singularities and $g$ may have stationary points. Our composite rule is defined on a mesh with $M$ subintervals and requires $MN+1$ evaluations of $f$. It satisfies an error estimate of the form $C_N k^{-r} M^{-N-1 + r}$, where $r$ is determined by the strength of any singularity in $f$ and the order of any stationary points in $g$ and $C_N$ is a constant which is independent of $k$ and $M$, but depends on $N$. The regularity requirements on $f$ and $g$ are explicit in the error estimates. For fixed $k$, the rate of convergence of the rule as $M \rightarrow \infty$ is the same as would be obtained if $f$ was smooth. Moreover, the quadrature error decays at least as fast as $k \rightarrow \infty$ as does the original integral $I_{k}^{[a,b]}(f,g)$. For the case of nonlinear oscillators $g$, the algorithm requires the evaluation of $g^{-1}$ at non-stationary points. Numerical results demonstrate the sharpness of the theory. An application to the implementation of boundary integral methods for the high-frequency Helmholtz equation is given.

math.NA↗
arXiv2011

On the q-Euler numbers and polynomials with weight 0

The purpose of this paper is to investigate some properties of q-Euler numbers and polynomials with weight 0. From those q-Euler numbers with weight 0, we derive some identities on the q-Euler numbers and polynomials with weight 0.

math.NT↗
arXiv2011

Bernstein polynomials on Simplex

We prove two identities for multivariate Bernstein polynomials on simplex, which are considered on a pointwise. In this paper, we study good approximations of Bernstein polynomials for every continuous functions on simplex and the higher dimensional q-analogues of Bernstein polynomials on simplex

math.NT↗
arXiv2011

On q-Berstein and q-Hermite polynomials

In this paper, we investigate the properties of q-Hermite polynomials related to q-Bernstein polynomials. From these properties, we derive some interesting relations between q-Berstein polynomials and q-Hermite polynomials.

math.NT↗