Showing papers by "Young Jin Suh published in 2016"
TL;DR: In this paper, it was shown that a Ricci simple manifold with vanishing divergence of the conformal curvature tensor admits a proper concircular vector field and it is necessarily a generalized Robertson-Walker space-time.
Abstract: A generalized Robertson–Walker (GRW) space-time is the generalization of the classical Robertson–Walker space-time. In the present paper, we show that a Ricci simple manifold with vanishing divergence of the conformal curvature tensor admits a proper concircular vector field and it is necessarily a GRW space-time. Further, we show that a stiff matter perfect fluid space-time or a mass-less scalar field with time-like gradient and with divergence-free Weyl tensor are GRW space-times.
50 citations
TL;DR: In this article, the authors introduced the notion of harmonic curvature for real hypersurfaces in the complex quadric Q m = S O m + 2 /S O m S O 2.
38 citations
TL;DR: Lobectomy plus isthmusectomy may be optimal for early-stage, node-negative papillary thyroid carcinoma originating in the isthmus for tumors ≤1 cm; total thyroidectomy might be better for tumors >1 cm.
Abstract: Background
The association between surgical extent and prognosis in papillary thyroid carcinoma originating in the isthmus is unclear.
23 citations
TL;DR: In this article, the authors introduced the notion of commuting Ricci tensor for real hypersurfaces in the complex quadric, and showed that the commuting tensor gives that the unit normal vector field becomes the principal or isotropic.
Abstract: We introduce the notion of commuting Ricci tensor for real hypersurfaces in the complex quadric $Q^m = SO_{m+2}/SO_mSO_2$. It is shown that the commuting Ricci tensor gives that the unit normal vector field~$N$ becomes $\frak A$-principal or $\frak A$-isotropic. Then according to each case, we give a complete classification of Hopf real hypersurfaces in $Q^m = SO_{m+2}/SO_mSO_2$ with commuting Ricci tensor.
21 citations
TL;DR: In this article, a complete classification of pseudo-Z symmetric space-times with harmonic conformal curvature tensors is presented, and a complete algebraic classification for the Weyl tensor is provided for n = 4.
Abstract: In this paper we present some new results about n(≥ 4)-dimensional pseudo-Z symmetric space-times. First we show that if the tensor Z satisfies the Codazzi condition then its rank is one, the space-time is a quasi-Einstein manifold, and the associated 1-form results to be null and recurrent. In the case in which such covector can be rescaled to a covariantly constant we obtain a Brinkmann-wave. Anyway the metric results to be a subclass of the Kundt metric. Next we investigate pseudo-Z symmetric space-times with harmonic conformal curvature tensor: a complete classification of such spaces is obtained. They are necessarily quasi-Einstein and represent a perfect fluid space-time in the case of time-like associated covector; in the case of null associated covector they represent a pure radiation field. Further if the associated covector is locally a gradient we get a Brinkmann-wave space-time for n > 4 and a pp-wave space-time in n = 4. In all cases an algebraic classification for the Weyl tensor is provided for n = 4 and higher dimensions. Then conformally flat pseudo-Z symmetric space-times are investigated. In the case of null associated covector the space-time reduces to a plane wave and results to be generalized quasi-Einstein. In the case of time-like associated covector we show that under the condition of divergence-free Weyl tensor the space-time admits a proper concircular vector that can be rescaled to a time like vector of concurrent form and is a conformal Killing vector. A recent result then shows that the metric is necessarily a generalized Robertson–Walker space-time. In particular we show that a conformally flat (PZS)n, n ≥ 4, space-time is conformal to the Robertson–Walker space-time.
20 citations
TL;DR: In this paper, it was shown that a pseudo-projectively flat spacetime with vanishing pseudoprojective curvature tensor obeys Einstein's field equation without cosmological constant is an Euclidean space.
Abstract: The object of the present paper is to study spacetimes admitting pseudo-projective curvature tensor. At first we prove that a pseudo-projectively flat spacetime is Einstein and hence it is of constant curvature and the energy momentum tensor of such a spacetime satisfying Einstein’s field equation with cosmological constant is covariant constant. Next, we prove that if the perfect fluid spacetime with vanishing pseudo-projective curvature tensor obeys Einstein’s field equation without cosmological constant, then the spacetime has constant energy density and isotropic pressure, and the perfect fluid always behaves as a cosmological constant and also such a spacetime is infinitesimally spatially isotropic relative to the unit timelike vector field
U. Moreover, it is shown that a pseudo-projectively flat spacetime satisfying Einstein’s equation without cosmological constant for a purely electromagnetic distribution is an Euclidean space. We also prove that under certain conditions a perfect fluid spacetime with divergence-free pseudo-projective curvature is a Robertson-Walker spacetime and the possible local cosmological structure of such a spacetime is of type I, D or O. We also study dust-like fluid spacetime with vanishing pseudo-projective curvature tensor.
15 citations
TL;DR: It is found that several factors, such as tumor size, lymphovascular invasion, and the Ki-67 index, are independent factors that predict positive ALNM on multivariate analysis for the patients with cT1–2 breast cancer.
15 citations
TL;DR: A target volume expansion of 10 mm from surgical clips may be sufficient to compensate for the displacement of clips during postoperative radiotherapy after breast-conserving surgery.
Abstract: PURPOSE Surgical clips are used as a target for postoperative breast radiotherapy, and displacement of surgical clips would result in inaccurate delivery of radiation. We investigated the displacement range of surgical clips in the breast during postoperative radiotherapy following breast-conserving surgery. METHODS A total of 178 patients who received breast-conserving surgery and postoperative radiation of 59.4 Gy in 33 fractions to the involved breast for 6.5 weeks were included. Surgical clips were used to mark the lumpectomy cavity during breast-conserving surgery. Patients undertook planning computed tomography (CT) scan for whole breast irradiation. Five weeks after beginning radiation, when the irradiation dose was 45 Gy, planning CT scan was performed again for a boost radiotherapy plan in all patients. The surgical clips were defined in both CT images and compared in lateromedial (X), anteroposterior (Y), superoinferior (Z), and three-dimensional directions. RESULTS The 90th percentile of displacement of surgical clips was 5.31 mm (range, 0.0-22.2 mm) in the lateromedial direction, 7.1 mm (range, 0.0-14.2 mm) in the anteroposterior direction, and 6.0 mm (range, 0.0-10.0 mm) in the superoinferior direction. The 90th percentile of three-dimensional displacement distance was 9.8 mm (range, 0.0-28.2 mm). On the multivariate analysis, seroma ≥15 mL was the only independent factor associated with the displacement of surgical clips. In patients with seroma ≥15 mL, the 90th percentile of displacement of surgical clips was 15.1 mm in the lateromedial direction, 12.7 mm in the anteroposterior direction, 10.0 mm in the superoinferior direction, and 21.8 mm in the three-dimensional distance. CONCLUSION A target volume expansion of 10 mm from surgical clips may be sufficient to compensate for the displacement of clips during postoperative radiotherapy after breast-conserving surgery. For patients who had a seroma, a replanning CT scan for a boost radiation should be considered to ensure exact postoperative radiotherapy in breast cancer.
15 citations
TL;DR: In Korean IDC patients with axillary lymph node metastasis, LIQ tumor location was associated with poor prognosis among those with HER2 and TN molecular subtypes and especially in those with more than T2 stage.
Abstract: Previous studies have not considered the axillary lymph node status when investigating the prognostic role of tumor location according to each molecular subtype. The present study aimed to investigate the prognostic implication of tumor location according to each molecular subtype in Korean invasive ductal carcinoma (IDC) patients with axillary lymph node metastasis. Data from 7856 Korean IDC women with axillary lymph node metastasis were retrospectively analyzed. According to tumor location, patients were divided into the following groups: upper-outer quadrant, lower-outer quadrant, upper-inner quadrant, lower-inner quadrant (LIQ), and central group. Overall survival (OS) and breast cancer-specific survival (BCSS) were evaluated according to tumor location and molecular subtype. A subgroup analysis based on tumor size categorization was also performed. The patients' mean age was 47.97 ± 9.64 years, and the median follow-up time was 90 months. The LIQ group showed significantly worse prognosis in OS and BCSS (76.4 and 83.3 %, respectively) compared with the other groups, which was only significant in human epidermal growth factor receptor 2 (HER2) overexpression and triple-negative (TN) subtypes. In the subgroup analysis according to tumor size, the LIQ group showed a significantly worse prognosis in OS and BCSS compared with the other groups, in HER2 and TN subtypes, and only in patients with more than T2 stage. In Korean IDC patients with axillary lymph node metastasis, LIQ tumor location was associated with poor prognosis among those with HER2 and TN molecular subtypes and especially in those with more than T2 stage.
12 citations
TL;DR: With thyroid carcinoma the decision to use radioactive iodine (RAI) ablation depends on the risk of poor outcomes, and the definition of minimal ETE is too broad, as it encompasses both microscopic invasion of the thyroid capsule and macroscopic invasion ofThe sternothyroid muscle.
Abstract: Aim
With thyroid carcinoma the decision to use radioactive iodine (RAI) ablation depends on the risk of poor outcomes. Although extrathyroid extension (ETE) is well known as a risk of poor outcomes for papillary thyroid carcinoma (PTC), the definition of minimal ETE is too broad, as it encompasses both microscopic invasion of the thyroid capsule (capsular invasion [CI]) and macroscopic invasion of the sternothyroid muscle.
Methods
We conducted a retrospective study to analyze the prognostic benefit of RAI ablation according to the presence of CI in a consecutive series of patients with PTC between October 1997 and December 2008. We studied two groups of patients, including those who received RAI (group I, n = 121) and those who did not (group II, n = 108). During follow-up, we assessed the locoregional recurrence of all patients.
Results
There were no statistically significant difference between the groups regarding locoregional recurrence at follow-up (13.2% for group I vs 9.3% for group II, P = 0.441). The association between RAI and locoregional recurrence in PTC patients with CI remained insignificant after adjusting for potential confounders, such as age, tumor size, sex, lymphatic invasion, vascular invasion and tumor multiplicity (P = 0.409, hazard ratio = 0.698, 95% confidence interval, 0.298–1.639).
Conclusions
This retrospective study suggests that RAI treatment is not associated with less locoregional recurrence in PTC patients who only demonstrate CI, although further prospective studies are required to confirm these findings.
11 citations
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TL;DR: In this article, a new commuting condition between the structure Jacobi operator and symmetric (1, 1)-type tensor field was introduced, that is, $R ''xi''phi T=TR ''xi''.
Abstract: In this paper, we introduce a new commuting condition between the structure Jacobi operator and symmetric (1,1)-type tensor field $T$, that is, $R_{\xi}\phi T=TR_{\xi}\phi$, where $T=A$ or $T=S$ for Hopf hypersurfaces in complex hyperbolic two-plane Grassmannians. By using simultaneous diagonalzation for commuting symmetric operators, we give a complete classification of real hypersurfaces in complex hyperbolic two-plane Grassmannians with commuting condition respectively.
TL;DR: In this article, a new commuting condition between the structure Jacobi operator and symmetric (1, 1)-type tensor field T was introduced, where T = A or T = S for Hopf hypersurfaces in complex hyperbolic two-plane Grassmannians.
Abstract: In this paper, we introduce a new commuting condition between the structure Jacobi operator and symmetric (1,1)-type tensor field T, that is, \({R_{\xi} \phi T = TR_{\xi} \phi}\), where T = A or T = S for Hopf hypersurfaces in complex hyperbolic two-plane Grassmannians. Using simultaneous diagonalization for commuting symmetric operators, we give a complete classification of real hypersurfaces in complex hyperbolic two-plane Grassmannians with commuting condition, respectively.
TL;DR: In this article, weakly cyclic Z symmetric spacetimes satisfying the condition div ={C=0} = 0} and conversely, conformally flat spacetime properties were investigated.
Abstract: The object of the present paper is to study weakly cyclic Z symmetric spacetimes At first we prove that a weakly cyclic Z symmetric spacetime is a quasi Einstein spacetime Then we study $${{(WCZS)}_{4}}$$
spacetimes satisfying the condition div $${C=0}$$
Next we consider conformally flat $${{(WCZS)}_{4}}$$
spacetimes Finally, we characterise dust fluid and viscous fluid $${{(WCZS)}_{4}}$$
spacetimes
TL;DR: In this paper, the curvature tensor of a real hypersurface M in complex hyperbolic two-plane Grassmannians SU 2, m/S (U 2 ⋅ U m ), m ≥ 2 from the equation of Gauss was derived.
Abstract: In this paper we first introduce the full expression of the curvature tensor of a real hypersurface M in complex hyperbolic two-plane Grassmannians SU 2 , m / S ( U 2 ⋅ U m ) , m ≥ 2 from the equation of Gauss. Next we derive a new formula for the Ricci tensor S of M in SU 2 , m / S ( U 2 ⋅ U m ) . Finally we give a complete classification of Hopf hypersurfaces in complex hyperbolic two-plane Grassmannians SU 2 , m / S ( U 2 ⋅ U m ) with Reeb invariant Ricci tensor, that is, L ξ S = 0 . Each can be described as a tube over a totally geodesic SU 2 , m − 1 / S ( U 2 ⋅ U m − 1 ) in SU 2 , m / S ( U 2 ⋅ U m ) or a horosphere whose center at infinity is singular.
TL;DR: In this article, the authors introduced the notion of commuting and parallel Ricci tensor for real hypersurfaces in the complex quadric Q m = S O m + 2 /S O 2 S O O m.
TL;DR: In this article, the Reeb parallel Ricci tensor was introduced for homogeneous real hypersurfaces in complex hyperbolic two-plane Grassmannians, which has a remarkable geometric structure as a Hermitian symmetric space.
Abstract: In this paper, we introduce the notion of Reeb parallel Ricci tensor for homogeneous real hypersurfaces in complex hyperbolic two-plane Grassmannians which has a remarkable geometric structure as a Hermitian symmetric space of rank 2. By using a new method of simultaneous diagonalizations, we give a complete classification for real hypersurfaces in complex hyperbolic two-plane Grassmannians with the Reeb parallel Ricci tensor.
TL;DR: The full expression of the curvature tensor of a real hypersurface M in complex hyperbolic two-plane Grassmannians SU 2, m / S ( U 2 ⋅ U m ) is introduced and it is proved that there do not exist Einstein Hopf or Q ⊥ -invariant Einstein real hypersures in SU 2.
TL;DR: All of real hypersurfaces M with Reeb invariant shape operator in the complex hyperbolic two-plane Grassmannians S U 2, m / S ( U 2 ź U m ) , m ź 2 are classified.
TL;DR: In this paper, a generalized Tanaka-Webster Reeb parallel Ricci tensor tensor for Hopf hypersurfaces was introduced. And the authors gave a complete classification of Hopf hypergraphs in the Levi-Civita connection.
Abstract: There are several kinds of classification problems for real hypersurfaces in complex two-plane Grassmannians . Among them, Suh classified Hopf hypersurfaces in with Reeb parallel Ricci tensor in Levi–Civita connection. In this paper, we introduce the notion of generalized Tanaka–Webster Reeb parallel Ricci tensor for Hopf hypersurfaces in . Next, we give a complete classification of Hopf hypersurfaces in with Reeb parallel Ricci tensor.
TL;DR: In this article, the authors considered a real hypersurface M in a complex two-plane Grassmannian and proved that M is an open part of a tube around a totally geodesic.
Abstract: Using GTW connection, we considered a real hypersurface M in a complex two-plane Grassmannian \({G_{2}({\mathbb{C}}^{m+2})}\) when the GTW Reeb Lie derivative of the structure Jacobi operator coincides with the Reeb Lie derivative. Next using the method of simultaneous diagonalization, we prove a complete classification for a real hypersurface in \({G_{2}({\mathbb{C}}^{m+2})}\) satisfying such a condition. In this case, we have proved that M is an open part of a tube around a totally geodesic \({G_{2}({\mathbb{C}}^{m+1})}\) in \({G_{2}({\mathbb{C}}^{m+2})}\).
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TL;DR: In this article, it was shown that real hypersurfaces with isometric Reeb flow in complex hyperbolic quadrics do not have any isometry in odd-dimensional complex quadrics.
Abstract: We classify real hypersurfaces with isometric Reeb flow in the complex hyperbolic quadrics ${Q^*}^{m} = SO^{o}_{2,m}/SO_mSO_2$, $m \geq 3$. We show that $m$ is even, say $m = 2k$, and any such hypersurface becomes an open part of a tube around a $k$-dimensional complex hyperbolic space ${\mathbb C}H^k$ which is embedded canonically in ${Q^*}^{2k}$ as a totally geodesic complex submanifold or a horosphere whose center at infinity is $\frak A$-isotropic singular. As a consequence of the result, we get the non-existence of real hypersurfaces with isometric Reeb flow in odd-dimensional complex quadrics ${Q^*}^{2k+1}$, $k \geq 1$.
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TL;DR: In this article, the notion of parallel structure Jacobi operator for real hypersurfaces in the complex quadric was introduced and a complete classification of real hypersuran surfaces with and without the Jacobi operators was given.
Abstract: First we introduce the notion of parallel structure Jacobi operator for real hypersurfaces in the complex quadric $Q^m = SO_{m+2}/SO_mSO_2$ . Next we give a complete classification of real hypersurfaces in $Q^m = SO_{m+2}/SO_mSO_2$ with parallel structure Jacobi operator.