• Bulletin of the Korean Mathematical Society
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• v.53 no.5
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• pp.1471-1481
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• 2016

We characterize reducing subspaces of weighted shifts with operator weights as wandering invariant subspaces of the shifts with additional structures. We show how some earlier results on reducing subspaces of powers of weighted shifts with scalar weights on the unit disk and the polydisk can be fitted into our general framework.

• Bulletin of the Korean Chemical Society
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• v.14 no.4
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• pp.500-506
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• 1993

$^1H$ and $^{13}C$ NMR spectra for pyridine, ${\beta}$-and ${\gamma}$-picoline, pyrazine, and 4,4'-bipyridyl complexed with paramagnetic undecatungstocobalto(II)silicate and undecatungstonickelo(II)silicate anions are reported. For these complexes the ligand exchange is slow on the NMR time scale and the pure resonance lines have been observed at room temperature. The isotropic shifts in nickel complexes can be interpreted in terms of contact shifts by ${\sigma}$-electron delocalization. Both contact and pseudocontact shifts contribute to the isotropic shifts in cobalt complexes. The contact shifts, which are obtained by subtracting the pseudocontact shifts from the isotropic shifts, require both ${\sigma}$-and ${\pi}$-electron delocalization from the cobalt ion. Slow ligand exchange has also allowed us to identify the species formed when bidentate ligands react with the heteropolyanions. Pyrazine forms a 1 : 1 complex, while 4,4'-bipyridyl forms both 1 : 1 and dumbbell-shaped 1 : 2 complexes.

• Bulletin of the Korean Mathematical Society
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• v.54 no.2
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• pp.633-646
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• 2017

Recently, Curto, Lee and Yoon considered the properties (such as, hyponormality, subnormality, and flatness, etc.) for 2-variable weighted shifts and constructed several families of commuting pairs of subnormal operators such that each family can be used to answer a conjecture of Curto, Muhly and Xia negatively. In this paper, we consider the weak and quadratic hyponormality of 2-variable weighted shifts ($W_1,W_2$). In addition, we detect the weak and quadratic hyponormality with some interesting 2-variable weighted shifts.

• Journal of the Korean Mathematical Society
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• v.51 no.2
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• pp.363-382
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• 2014

In this paper we first characterize the hereditarily hypercyclicity of the unilateral (or bilateral) weighted shifts on the spaces $L^2(\mathbb{N},\mathcal{K})$ (or $L^2(\mathbb{Z},\mathcal{K})$) with weight sequence {$A_n$} of positive invertible diagonal operators on a separable complex Hilbert space $\mathcal{K}$. Then we give the necessary and sufficient conditions for the supercyclicity of those weighted shifts, which extends some previous results of H. Salas. At last, we give some conditions for the supercyclicity of three different weighted shifts.

• Korean Journal of Mathematics
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• v.17 no.3
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• pp.293-298
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• 2009

In this paper we make a connection between the specific class of weighted shifts and general study of k-hyponormality. We show how the k-hyponormality of an arbitrary operator can be ascertained by examining the k-hyponormality of an associated family of weighted shifts.

• Journal of the Chungcheong Mathematical Society
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• v.29 no.1
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• pp.123-135
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• 2016

In this article, we introduce the transforms of Pythagorean and quadratic means of weighted shifts. We then explore how the transforms of weighted shifts behaves, in comparison with the Aluthge transform.

• Bulletin of the Korean Chemical Society
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• v.18 no.10
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• pp.1090-1093
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• 1997

The solvent effects on the isotropic NMR shifts in conformationally rigid ligands such as quinuclidine, pyridine, and 4-aminopyridine coordinated to the paramagnetic polyoxometalate, [SiW11CoⅡO39]6- (SiW11Co), are reported. For these complexes the ligand exchange is slow on the NMR time scale and pure 1H NMR signals have been observed at room temperature. The signals for the SiW11Co complexes are shifted upfield whe dimethyl sulfoxide-d6 (DMSO) is added to a D2O solution. The isotropic shifts are separated into contact and pseudocontact contributions by assuming that the contact shifts are proportional to the isotropic shifts of the same ligands coordinated to [SiW11NiⅡO39]6-. It is shown that both the contact and pseudocontact shifts decrease (the absolute values of the pseudocontact shifts increase), when D2O is replaced by DMSO. It is suggested that D2O, a strong hydrogen bond donor, withdraws electron density from [SiW11CoⅡO39]6-, increasing the acidity of the cobalt ion toward the axial ligand. When D2O is replaced by DMSO, the acidity of the cobalt ion in SiW11Co decreases, weakening the Co-N bond. Then both the contact and pseudocontact shifts are expected to decrease in agreement with the observed solvent effects.

• Journal of Korean Clinical Nursing Research
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• v.19 no.3
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• pp.309-320
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• 2013

Purpose: This study was conducted to identify relationships among circadian types, sleep quality, and adaptation to night shifts among nurses working on two or three day night duties. Methods: The participants were 199 ward nurses from two university hospitals in Gyeongnam province. Each nurse worked on two or three day night duties. Data were collected between September 24 and October 14, 2012 and analyzed using t-test, ANOVA, $Scheff{\grave{e}}$ test, Pearson correlation, and multiple regression with SPSS/WIN 14.0 program. Results: Mean scores for sleep quality and adaptation to night shifts was $4.92{\pm}1.46$ on a 10-point scale and $2.66{\pm}0.47$ on a 5-point scale respectively. There were no significant differences in sleep quality and adaptation to night shifts according to circadian types of nurses. There were significant correlation between sleep quality and adaptation to night shifts (r=.25, p<.001). Factors affecting adaptation to night shifts were preference for night shifts, and subjective health status, which together explained about 35% of the total variance. Conclusions: Nurses working on two or three day night duties had low level of sleep quality and adaptation to night shifts. It is necessary to improve preference for night shifts and subjective health status for improving adaptation to night shifts of nurse.

• Korean System Dynamics Review
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• v.5 no.1
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• pp.127-142
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• 2004

Feedback loop dominance is a key concept to understand structural driving forces of system behavior. In this paper, we propose two kinds of shifts in dominant feedback loops: continuous shifts (CS) and discrete shifts (DS). With the help of questionnaires, we verified three hypotheses regarding cognitive biases in perceiving the shifts in dominant feedback loops: 1) failure in perceiving continuous shifts, 2) tendency of decision making based on discrete shifts, and 3) different perception on the dominant feedback loops between level variables and rate variables. We discussed the implication of these cognitive biases on time delay and timing strategy in decision-making processes.

• Journal of the Chungcheong Mathematical Society
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• v.27 no.1
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• pp.99-103
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• 2014

In this paper, we characterize the m-isometric weighted shifts, using this characterization, we study the relations between the hyponormality and the m-isometricity of operators.