Kyungpook National University

About: Kyungpook National University is a education organization based out in Daegu, South Korea. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 20497 authors who have published 42107 publications receiving 834608 citations.

Second-order perturbations of the Friedmann world model

Abstract: We consider the instability of the Friedmann world model to second order in perturbations. We present the perturbed set of equations up to second order in the Friedmann background world model with a general spatial curvature and cosmological constant. We consider systems with completely general imperfect fluids, minimally coupled scalar fields, an electromagnetic field, and generalized gravity theories. We also present the case of null geodesic equations, and one based on the relativistic Boltzmann equation. In due time, a decomposition is made for scalar-, vector-, and tensor-type perturbations which couple with each other to second order. A gauge issue is resolved to each order. The basic equations are presented without imposing any gauge condition, and thus in a gauge-ready form so that we can take full advantage of having gauge freedom in analyzing the problems. As an application we show that to second order in perturbation the relativistic pressureless ideal fluid of the scalar type reproduces exactly the known Newtonian result. As another application we rederive the large-scale conserved quantities (of the pure scalar and tensor perturbations) to second order, first shown by Salopek and Bond, now from the exact equations. Several other applications are shown as well.

Complete amplitude and phase control of light using broadband holographic metasurfaces

Abstract: Reconstruction of light profiles with amplitude and phase information, called holography, is an attractive optical technology with various significant applications such as three-dimensional imaging and optical data storage. Subwavelength spatial control of both amplitude and phase of light is an essential requirement for an ideal hologram. However, traditional holographic devices suffer from their restricted capabilities of incomplete modulation in both amplitude and phase of visible light; this results in sacrifice of optical information and undesirable occurrences of critical noises in holographic images. Herein, we have proposed a novel metasurface that is capable of completely controlling both the amplitude and phase profiles of visible light independently with subwavelength spatial resolution. The full, continuous, and broadband control of both amplitude and phase was achieved using X-shaped meta-atoms based on the expanded concept of the Pancharatnam-Berry phase. The first experimental demonstrations of the complete complex-amplitude holograms with subwavelength definition at visible wavelengths were achieved, and excellent performances with a remarkable signal-to-noise ratio as compared to those of traditional phase-only holograms were obtained. Extraordinary control capability with versatile advantages of our metasurface paves a way to an ideal holography, which is expected to be a significant advancement in the field of optical holography and metasurfaces.

Exosomes Derived From Natural Killer Cells Exert Therapeutic Effect in Melanoma.

Abstract: Objective: Exosomes are nanovesicles that are released from normal and tumor cells and are detectable in cell culture supernatant and human biological fluids. Although previous studies have explored exosomes released from cancer cells, little is understood regarding the functions of exosomes released by normal cells. Natural killer (NK) cells display rapid immunity to metastatic or hematological malignancies, and efforts have been undertaken to clinically exploit the antitumor properties of NK cells. However, the characteristics and functions of exosomes derived from NK cells remain unknown. In this study, we explored NK cell-derived exosome-mediated antitumor effects against aggressive melanoma in vitro and in vivo. Methods: B16F10 cells were transfected with enhanced firefly luciferase (effluc) and thy1.1 genes, and thy1.1-positive cells were immunoselected using microbeads. The resulting B16F10/effluc cells were characterized using reverse transcriptase polymerase chain reaction (RT-PCR), western blotting, and luciferase activity assays. Exosomes derived from NK-92MI cells (NK-92 Exo) were isolated by ultracentrifugation and density gradient ultracentrifugation. NK-92 Exo were characterized by transmission electron microscopy and western blotting. We also performed an enzyme-linked immunosorbent assay to measure cytokines retained in NK-92 Exo cells. The in vitro cytotoxicity of NK-92 Exo against the cancer cells was determined using a bioluminescence imaging system (BLI) and CCK-8 assays. To investigate the possible side effects of NK-92 Exo on healthy cells, we also performed the BLI and CCK-8 assays using the human kidney Phoenix™-Ampho cell line. Flow cytometry and western blotting confirmed that NK-92 Exo induced apoptosis in the B16F10/effluc cells. In vivo, we used a B16F10/effluc cell xenograft model to detect the immunotherapeutic effect of NK-92 Exo. We injected NK-92 Exo into tumors, and tumor growth progression was monitored using the IVIS Lumina imaging system and ultrasound imaging. Tumor mass was monitored after in vivo experiments. Results: RT-PCR and western blotting confirmed effluc gene expression and protein levels in B16F10/effluc cells. B16F10/effluc activity was found to increase with increasing cell numbers, using BLI assay. For NK-92 Exo characterization, western blotting was performed on both ultracentrifuged and density gradient-isolated exosomes. The results confirmed that NK cell-derived exosomes express two typical exosome proteins, namely CD63 and ALIX. We demonstrated by western blot analysis that NK-92 Exo presented two functional NK proteins, namely perforin and FasL. Moreover, we confirmed the membrane expression of FasL. The enzyme-linked immunosorbent assay results indicated that NK-92 Exo can secrete tumor necrosis factor (TNF)-α, which affected the cell proliferation signaling pathway. The antitumor effect of NK-92 Exo against B16F10/effluc cells in vitro was confirmed by BLI (p < 0.001) and CCK-8 assays (p < 0.001). Furthermore, in normal healthy cells, even after 24 h of co-culture, NK-92 Exo did not exhibit significant side effects. In the in vivo experiments, tumors in the vehicle control group were significantly increased, compared with those in the NK-92 Exo-treated group (p < 0.05). Conclusion: The results of the current study suggest that exosomes derived from NK cells exert cytotoxic effects on melanoma cells and thus warrant further development as a potential immunotherapeutic strategy for cancer.

Physicochemical Characteristics of Self-Assembled Nanoparticles Based on Glycol Chitosan Bearing 5β-Cholanic Acid

Abstract: The self-aggregation behavior and microscopic characteristics of hydrophobically modified glycol chitosans (HGCs), prepared by covalent attachment of 5β-cholanic acid to glycol chitosan, were investigated by using 1H NMR, dynamic light scattering, fluorescence spectroscopy, and transmission electron microscopy (TEM). The HGCs formed self-aggregates in an aqueous phase by intra- or intermolecular association between hydrophobic 5β-cholanic acids attached to glycol chitosan. The critical aggregation concentrations (cacs) of the HGCs were dependent on the degree of substitution (DS) of 5β-cholanic acid and were significantly lower than those of low molecular weight surfactants. The mean diameters of the self-aggregates decreased with the increase in the DS of 5β-cholanic acid because of the formation of compact hydrophobic inner cores. The TEM images demonstrated that the shape of the self-aggregates, on the basis of the HGCs, is spherical. The partition equilibrium constants (Kv) of pyrene, measured in the ...