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Ghim, Sa-Youl Korean Society of Life Science 2001 Journal of Life Science Vol.11 No.2
The pyrR gene of the pyrimidine biosynthesis (pyr) operon of the thermophile Bacillus caldolyticus, encoding a uracil phosphoribosyltransferase (UPRTase), turned to rely as a pyr operon regulator. It has been proposed that PyrR mediates transcriptional termination-antitermination at three intercistronic regions of the par operon (S.-Y Ghim and J. Neuhard, J. Bacteriol.,176, 3698-3707, 1994). In this research, a plasmid carrying the pyrR region of B. caldolyticus could restore a pyrimidine regulation in a pyrR mutant of B. subtilis. Expression of pyrR was found to increase 6-7 fold during pyrimidine starvation. Additionally, a highly conserved nucleotide sequence which may constitute the binding site for a PyrR protein (PyrR-binding loop) in transcript was staggested. Alternative antiterminator and terminator structures involving three conserved motifs in front of the pyrR, pyrP and pyrB genes, respectively, are proposed to account for the observed regulation pattern.
Spectrally resolved white-light interferometry for 3D inspection of a thin-film layer structure
Ghim, Young-Sik,Kim, Seung-Woo The Optical Society 2009 Applied Optics Vol.48 No.4
<P>We describe an improved scheme of spectrally resolved white-light interferometry, which provides 3D visual inspection of a thin-film layer structure with nanometer level resolutions. Compared to the authors' previous method [Appl. Phys. Lett.91, 091903 (2007)APPLAB0003-695110.1063/1.2776015], 3D tomographic information of thin films can be obtained by decoupling the film thickness and top surface profile, which is embodied by inducing spectral carrier frequency to the reference arm and applying a low-pass filter to the interferogram instead of two troublesome measurement steps of activating and deactivating a mechanical shutter. We test and verify our proposed method by measuring a patterned thin-film layer structure as well as standard specimens of thin films with various thicknesses.</P>
Condensation heat transfer of low GWP ORC working fluids in a horizontal smooth tube
Ghim, G.,Lee, J. Pergamon Press ; Elsevier Science Ltd 2017 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.104 No.-
The objective of the current study is to conduct an experimental investigation of condensation heat transfer for the ORC (organic Rankine cycle) working fluids R245fa, Novec®649 and HFE-7000 over a wide range of parameters. Quasi-local condensation heat transfer coefficients are measured in a straight horizontal 7.75-mm-ID smooth tube with flow conditions at mass flux G=150-700kg (m<SUP>2</SUP>-s)<SUP>-1</SUP>, local equilibrium quality x=0.05-0.95, and reduced pressure, P<SUB>r</SUB>=0.05-0.15. Test data reveal that the environmentally friendly fluids have lower condensation heat transfer coefficients when compared to R245fa. The 141 measured condensation heat transfer coefficients are compared to six well-known correlations. Among the six correlations verified with test data, the Shah correlation shows the best predictive performance for the three fluids tested.
Ghim, G.,Lee, J. Pergamon ; Elsevier Science Ltd 2016 Applied thermal engineering Vol.106 No.-
The existence of temperature gliding in non-azeotropic mixture working fluids provides a promising opportunity for greatly improved resource utilization in organic Rankine cycle (ORC) systems for geothermal applications. The condensation heat transfer degradation associated with working fluid mixtures is an unavoidable penalty that may reduce the utilization and system benefits by necessitating larger heat exchangers. The objective of the current study is an experimental investigation of condensation heat transfer for R245fa, n-pentane, and a composition of their mixture. Quasi-local condensation heat transfer coefficients are measured in a straight horizontal smooth tube with flow conditions at mass flux G=100 and 150kg(m<SUP>2</SUP>s)<SUP>-1</SUP>, local equilibrium quality x=0.05-0.80, and reduced pressures P<SUB>r</SUB>=0.05-0.15. The reduced condensation heat transfer coefficients from the test are compared with the predictions from already established mixture correction methods in the literature. Pure components R245fa and n-pentane condensation heat transfer data are well predicted by Shah (1979) correlations for all test conditions. However, their non-azeotropic mixture condensation heat transfer data require additional correction parameter to account for the heat transfer degradation. This correction parameter is correlated by the temperature gliding gradient of mixture fluids. Test data with mixture working fluids from current study are reasonably well predicted by the corrected in-tube correlation.
Endothelial Deletion of Phospholipase D2 Reduces Hypoxic Response and Pathological Angiogenesis
Ghim, Jaewang,Moon, Jin-Sook,Lee, Chang Sup,Lee, Junyeop,Song, Parkyong,Lee, Areum,Jang, Jin-Hyeok,Kim, Dayea,Yoon, Jong Hyuk,Koh, Young Jun,Chelakkot, Chaithanya,Kang, Byung Jun,Kim, Jung-Min,Kim, Ky American Heart Association, Inc. 2014 Arteriosclerosis, thrombosis, and vascular biology Vol.34 No.8
<P><B>Objective—</B></P><P>Aberrant regulation of the proliferation, survival, and migration of endothelial cells (ECs) is closely related to the abnormal angiogenesis that occurs in hypoxia-induced pathological situations, such as cancer and vascular retinopathy. Hypoxic conditions and the subsequent upregulation of hypoxia-inducible factor-1α and target genes are important for the angiogenic functions of ECs. Phospholipase D2 (PLD2) is a crucial signaling mediator that stimulates the production of the second messenger phosphatidic acid. PLD2 is involved in various cellular functions; however, its specific roles in ECs under hypoxia and in vivo angiogenesis remain unclear. In the present study, we investigated the potential roles of PLD2 in ECs under hypoxia and in hypoxia-induced pathological angiogenesis in vivo.</P><P><B>Approach and Results—</B></P><P><I>Pld2</I> knockout ECs exhibited decreased hypoxia-induced cellular responses in survival, migration, and thus vessel sprouting. Analysis of hypoxia-induced gene expression revealed that PLD2 deficiency disrupted the upregulation of hypoxia-inducible factor-1α target genes, including <I>VEGF</I>, <I>PFKFB3</I>, <I>HMOX-1</I>, and <I>NTRK2</I>. Consistent with this, PLD2 contributed to hypoxia-induced hypoxia-inducible factor-1α expression at the translational level. The roles of PLD2 in hypoxia-induced in vivo pathological angiogenesis were assessed using oxygen-induced retinopathy and tumor implantation models in endothelial-specific <I>Pld2</I> knockout mice. <I>Pld2</I> endothelial-specific knockout retinae showed decreased neovascular tuft formation, despite a larger avascular region. Tumor growth and tumor blood vessel formation were also reduced in <I>Pld2</I> endothelial-specific knockout mice.</P><P><B>Conclusions—</B></P><P>Our findings demonstrate a novel role for endothelial PLD2 in the survival and migration of ECs under hypoxia via the expression of hypoxia-inducible factor-1α and in pathological retinal angiogenesis and tumor angiogenesis in vivo.</P>
3D surface mapping of freeform optics using wavelength scanning lateral shearing interferometry.
Ghim, Young-Sik,Rhee, Hyug-Gyo,Davies, Angela,Yang, Ho-Soon,Lee, Yun-Woo Optical Society of America 2014 Optics express Vol.22 No.5
<P>Freeform optics have emerged as promising components in diverse applications due to the potential for superior optical performance. There are many research fields in the area ranging from fabrication to measurement, with metrology being one of the most challenging tasks. In this paper, we describe a new variant of lateral shearing interferometer with a tunable laser source that enables 3D surface profile measurements of freeform optics with high speed, high vertical resolution, large departure, and large field-of-view. We have verified the proposed technique by comparing our measurement result with that of an existing technique and measuring a representative freeform optic.</P>