S.C. Kim

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.

FTFD: an informatics pipeline supporting phylogenomic analysis of fungal transcription factors

SUMMARY Genomes of more than 60 fungal species have been sequenced to date, yet there has been no systematic approach to analyze fungal transcription factors (TFs) kingdom widely. We developed a standardized pipeline for annotating TFs in fungal genomes. Resulting data have been archived in a new database termed the Fungal Transcription Factor Database (FTFD). In FTFD, 31,832 putative fungal TFs, identified from 62 fungal and 3 Oomycete species, were classified into 61 families and phylogenetically analyzed. The FTFD will serve as a community resource supporting comparative analyses of the distribution and domain structure of TFs within and across species. AVAILABILITY All data described in this study can be browsed through the FTFD web site at http://ftfd.snu.ac.kr/.

Prognostic significance of signet ring cell carcinoma of the stomach

A retrospective analysis of 3,702 gastric cancer patients operated on between 1981 and 1991 was carried out to compare the clinicopathological features of signet ring cell (SRC) gastric cancer with other cell types. Four hundred and fifty patients (12.2%) had signet ring cell gastric carcinoma. There was a tendency for patients with the signet ring cell gastric cancer to be younger and female, and of the middle-third part of stomach to be involved. The proportion of early gastric cancers in signet ring cell gastric cancers was 43%, which was significantly higher than in the other histological types [33% in well differentiated (WD) type, 23% in moderately differentiated (MD) type, and 13% in poorly differentiated (PD) type]. Early stage signet ring cell gastric carcinomas were less invasive in depth and had less lymph node metastasis. However, signet ring cell gastric cancers in advanced stage were more invasive and had more lymph node metastasis than other cell types. There was no significant difference in five year survival rates (5YSR) among patients with different histological cell types in early stage gastric cancers. But, in advanced gastric cancers, the prognosis for patients with the signet ring cell type was significantly worse than for the other types (SRC, 31.9% 5YSR; WD, 45.1% 5YSR; MD, 38.4% 5YSR; PD, 34.5% 5YSR) (P < 0.05), which can be explained by the finding that advanced gastric cancers with signet ring cell type have a larger tumour size, more lymph node metastasis, a deeper invasive depth and more Borrmann type 4 lesions than other histological types. This study suggests that signet ring cell gastric cancer may have a different biological behaviour.

Novel artificial receptors for alkylammonium ions with remarkable selectivity and affinity

The benzene-based tripodal tris(oxazolines) have been developed as the most selective and strong receptors toward linear alkylammonium ions reported to date. Among six tris(oxazolines) based on 2,4,6-trimethylbenzene framework, the phenylglycinol-derived receptor 4 exhibits the largest association constant toward nBuNH3+ (logK(ass) = 6.65 +/- 0.02), while a similar value toward tBuNH3+, (logK(ass) = 3.80 +/- 0.01) compared with others, which corresponds to the selectivity ratio of nBuNH3+/tBuNH3+ as high as approximately equals 700. The tris(oxazoline) 6 that has bare oxazoline ring exhibits still a large association constant toward sterically hindered tBuNH3+ (logK(ass) = 5.26 +/- 0.02). Both receptors 4 and 6 extract beta-phenethylammonium ion from water into chloroform almost completely. When the benzene frame is changed from 2,4,6-trimethylbenzene to 2,4,6-triethylbenzene, dramatic changes in the affinity as well as in the selectivity are observed. The association constant observed by tris(oxazoline) 8 toward nBuNH3+ approaches 10(8)M(-1) and the selectivity ratio of nBuNH3+/tBuNH3+ is increased to 2,700. This selectivity is even more enhanced to 4,000 with tris(oxazoline) 9. The enhanced binding affinity and high selectivity observed with receptors 4 and related derivatives 7-9 compared with others can be explained by an optimized steric and electronic environment provided by the phenyl substituents, which has been unambiguously demonstrated by X-ray crystallographic and 1H NMR spectroscopic studies on the host-guest complexes. The new receptor system has several unique features such as ready availability, structural simplicity, and in particular, versatility in derivatization. By virtue of these advantages, it can be readily tailored as selective receptors toward biologically important amines.

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.

Neutron beam test of CsI crystal for dark matter search

Abstract We have studied the response of Tl- and Na-doped CsI crystals to nuclear recoils and γs below 10 keV . The response of CsI crystals to nuclear recoil was studied with mono-energetic neutrons produced by the 3 H ( p , n ) 3 He reaction. This was compared to the response to Compton electrons scattered by 662 keV γ-ray. Pulse shape discrimination between the response to these γs and nuclear recoils was studied, and quality factors were estimated. The quenching factors for nuclear recoils were derived for both CsI(Na) and CsI(Tl) crystals.Abstract We have studied the response of Tl- and Na-doped CsI crystals to nuclear recoils and γs below 10 keV . The response of CsI crystals to nuclear recoil was studied with mono-energetic neutrons produced by the 3 H ( p , n ) 3 He reaction. This was compared to the response to Compton electrons scattered by 662 keV γ-ray. Pulse shape discrimination between the response to these γs and nuclear recoils was studied, and quality factors were estimated. The quenching factors for nuclear recoils were derived for both CsI(Na) and CsI(Tl) crystals.

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 kg days data using one full-size CsI ( T l ) crystal of 6.6 kg mass.

Synthesis of chiral bis(oxazolinyl)biferrocene ligands and their application to Cu(I)-catalyzed asymmetric cyclopropanation

Abstract Homochiral bis(oxazolinyl)biferrocene ligands, which have both planar and central chirality, are synthesized from oxazolinylferrocenes through a diastereoselective directed lithiation followed by an oxidative dimerization. Asymmetric cyclopropanation of styrene with diazoacetates in the presence of 5 mol% CuOTf-bis(oxazolinyl)biferrocene complexes gives 2-(phenyl)cyclopropane carboxylates in up to 99% ee.

The Virtual Waiting Time of the M / G / 1 Queue with Impatient Customers

The M/G/1 queue with impatient customers is studied. The complete formula of the limiting distribution of the virtual waiting time is derived explicitly. The expected busy period of the queue is also obtained by using a martingale argument.