Jungil Lee

Using singular values to build a subgrid-scale model for large eddy simulations

An eddy-viscosity based, subgrid-scale model for large eddy simulations is derived from the analysis of the singular values of the resolved velocity gradient tensor. The proposed σ-model has, by construction, the property to automatically vanish as soon as the resolved field is either two-dimensional or two-component, including the pure shear and solid rotation cases. In addition, the model generates no subgrid-scale viscosity when the resolved scales are in pure axisymmetric or isotropic contraction/expansion. At last, it is shown analytically that it has the appropriate cubic behavior in the vicinity of solid boundaries without requiring any ad-hoc treatment. Results for two classical test cases (decaying isotropic turbulence and periodic channel flow) obtained from three different solvers with a variety of numerics (finite elements, finite differences, or spectral methods) are presented to illustrate the potential of this model. The results obtained with the proposed model are systematically equivalent...

Limits on WIMP-nucleon cross section with CsI(Tl) crystal detectors

The Korea Invisible Mass Search(KIMS) experiment presents new limits on WIMP-nucleon cross section using the data from an exposure of 3409 kgd taken with low background CsI(Tl) crystals at Yangyang underground laboratory. The most stringent limit on the spin dependent interaction for pure proton case is obtained. The DAMA signal region for both spin independent and spin dependent interactions for the WIMP mass higher than 20 GeV/c^2are excluded by the single experiment with crystal scintillators.

New Limits on Interactions between Weakly Interacting Massive Particles and Nucleons Obtained with CsI(Tl) Crystal Detectors

The Korea Invisible Mass Search (KIMS) experiment presents new limits on the weakly interacting massive particle (WIMP)-nucleon cross section using data from an exposure of 3409 kg.d taken with low-background CsI(Tl) crystals at the Yangyang Underground Laboratory. The most stringent limit on the spin-dependent interaction for a pure proton case is obtained. The DAMA signal region for both spin-independent and spin-dependent interactions for the WIMP masses greater than 20 GeV/c2 is excluded by the single experiment with crystal scintillators.

A dynamic subgrid-scale eddy viscosity model with a global model coefficient

In the present study, a dynamic subgrid-scale eddy viscosity model is proposed for large eddy simulation of turbulent flows in complex geometry. A subgrid-scale eddy viscosity model recently proposed by Vreman [Phys. Fluids 16, 3670 (2004)] which guarantees theoretically zero subgrid-scale dissipation for various laminar shear flows, is considered as a base model. A priori tests with the original Vreman model show that it predicts the correct profile of subgrid-scale dissipation in turbulent channel flow but the optimal model coefficient is far from universal. A dynamic procedure of determining the model coefficient is proposed based on the “global equilibrium” between the subgrid-scale dissipation and the viscous dissipation. An important feature of the proposed procedure is that the model coefficient determined is globally constant in space but varies only in time. A posteriori tests of the proposed dynamic model are conducted through large eddy simulations of forced isotropic turbulence at Reλ=103, tur...

CaMoO/sub 4/ scintillation crystal for the search of /sup 100/Mo double beta decay

Scintillation properties of calcium molybdate are investigated. The emission spectrum is broad with a maximum at 520 nm. At room temperature the light yield is 4% of CsI(Tl) (400 photoelectrons/MeV) and the decay time is 17 /spl mu/s. During cooling the light yield and decay time increase. Prospects of optimization of this scintillator are also discussed. The feasibility of the material for the search of neutrinoless double beta decay of /sup 100/Mo is analyzed. A half life limit of T/sub 1/2/=1/spl middot/10/sup 25/ years (68% CL) seems feasible with CaMoO/sub 4/ scintillator, running with 10 kg of /sup 100/Mo for 5 years. The background due to two neutrino double beta decay of /sup 48/Ca is also considered. Requirements for new scintillators for double beta decay search are formulated.

First limit on WIMP cross section with low background CsI(Tℓ) crystal detector

Abstract The Korea Invisible Mass Search (KIMS) Collaboration has been carrying out WIMP search experiment with CsI ( T l ) crystal detectors at the YangYang Underground Laboratory. A successful reduction of the internal background of the crystal was done and a good pulse shape discrimination was achieved. We report the first result on WIMP search obtained with 237 kgu2009days data using one full-size CsI ( T l ) crystal of 6.6 kg mass.

AMoRE experiment: a search for neutrinoless double beta decay of 100Mo isotope with 40Ca100MoO4 cryogenic scintillation detector

AMoRE (Advanced Mo based Rare process Experiment) collaboration is going to use calcium molybdate crystals as cryogenic scintillation detector in a search for neutrinoless DBD of 100Mo isotope. Simultaneous detection of phonons and light will be used to reject internal background. A FWHM resolution of 0.2% in the phonon channel has been achieved with a 0.5 cm3 crystal. Several 40Ca100MoO4 crystals (≈ 0.5 kg) have been developed from enriched 100Mo and depleted 40Ca materials. The light yield of these crystals has been shown to be comparable with reference CaMoO4 scintillators for temperatures ranging down to 8 K. The content of dangerous radioisotopes in the crystals is under measurement. The projected sensitivity of the experiment for a 250 kg × years exposure is lim T1/2 ~ 3 × 1026 years, which corresponds to the effective Majorana neutrino mass mv ~ 0.02 – 0.06 eV.

Dynamic global model for large eddy simulation of transient flow

In the present study, the dynamic subgrid-scale eddy viscosity models with a global model coefficient by Park et al. [Phys. Fluids 18, 125109 (2006)] (called dynamic global models hereafter) are applied to large eddy simulation of decaying isotropic turbulence to examine their performances in transient flow. The dynamic global model based on the global equilibrium between the subgrid-scale dissipation and the viscous dissipation fails to predict the temporal behavior of decaying isotropic turbulence. On the other hand, the dynamic global model based on the Germano identity shows an excellent agreement with the experimental data of decaying isotropic turbulence.

Inclusive S-wave charmonium productions in B decays.

The inclusive {ital S}-wave charmonium production rates in {ital B} decays are considered using the Bodwin-Braaten-Lepage approach, including the relativistic corrections and the color-octet mechanism suggested as a possible solution to the {psi}{prime} puzzle at the Fermilab Tevatron. We first consider relativistic and radiative corrections to {ital J}/{psi}{r_arrow}{ital e}{sup +}{ital e}{sup {minus}} and {ital J}/{psi}{r_arrow} light hadrons (LH{close_quote}s), in order to determine two nonperturbative parameters, {l_angle}{ital J}/{psi}{parallel}{ital O}{sub 1}({sup 3}{ital S}{sub 1}){parallel}{ital J}/{psi}{r_angle}, {l_angle}{ital J}/{psi}{parallel}{ital P}{sub 1}({sup 3}{ital S}{sub 1}){parallel}{ital J}/{psi}{r_angle}, in the factorization formulas for these decays. Using these two matrix elements and including the color-octet {ital c{bar c}}({sup 3}{ital S}{sub 1}) state contribution, we get a moderate increase in the decay rates for {ital B} decays into {ital J}/{psi} (or {psi}{prime})+{ital X}. Our results {ital B}({ital B}{r_arrow}{ital J}/{psi} (or {psi}{prime})+{ital X})=0.58 (0.23){percent} for {ital M}{sub {ital b}}=5.3 GeV get closer to the recent CLEO data. As a by-product, we prefer a larger decay rate for {eta}{sub {ital c}}{r_arrow}LH compared to the present data. {copyright} {ital 1996 The American Physical Society.}

Four quark operators relevant to B meson lifetimes from QCD sum rules

At the order of 1/m_b^3, the B meson lifetimes are controlled by the hadronic matrix elements of some four-quark operators. The nonfactorizable magnitudes of these four-quark operator matrix elements are analyzed by QCD sum rules in the framework of heavy quark effective theory. The vacuum saturation for color-singlet four-quark operators is justified at hadronic scale, and the nonfactorizable effect is at a few percent level. However for color-octet four-quark operators, the vacuum saturation is violated sizably that the nonfactorizable effect cannot be neglected for the B meson lifetimes. The implication to the extraction of some of the parameters from B decays is discussed. The B meson lifetime ratio is predicted as tau(B^-)/tau(B^0)=1.09pm 0.02. However, the experimental result of the lifetime ratio tau(Lambda_b)/tau(B^0) still cannot be explained.