Sang H Lee

Nathan Kline Institute, Orangeburg, New York, United States

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Publications (15)44.21 Total impact

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    ABSTRACT: In this study, we demonstrated that a reduction in solely the concentration of the polymer solution for preparation of the support layer effectively enhances the water flux of a thin-film composite (TFC) reverse osmosis (RO) membrane. However, a decrease in the polymer concentration caused the sub-surface structure of the support layer to become too porous, which unavoidably weakened the mechanical strength of the support layer. To overcome the problem, we prepared a highly porous support layer with improved mechanical strength by incorporating graphene oxide (GO) platelets. The thickness of the GO platelets was controlled by adjusting the mechanical energy input per volume of the precursor solution. We confirmed that well-exfoliated GO platelets (mean thickness: about 1.5 nm) are more effective in enhancing the mechanical properties of the support layer. The TFC RO membrane made of the GO composite support layer had almost 1.6 to 4 times higher water flux with comparable salt rejection compared to both the current upper bounds of the RO membranes prepared by modification of the active layer and commercial RO membranes.
    Journal of Materials Chemistry A 08/2015; 3(44). DOI:10.1039/C5TA04042F · 7.44 Impact Factor
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    ABSTRACT: Quorum quenching (QQ) with a microbial vessel has recently been reported as an economically feasible biofouling control platform in a membrane bioreactor (MBR) for wastewater treatment. In this study, a quorum quenching MBR with a ceramic microbial vessel (CMV) was designed to overcome the extremely low F/M ratio inside a microbial vessel. The CMV was prepared with a monolithic ceramic micro-porous membrane and AHL degrading QQ bacteria, Pseudomonas sp. 1A1. The 'inner flow feeding mode' was introduced, under which fresh feed was supplied to the MBR only through the center lumen in the CMV. The inner flow feeding mode facilitated nutrient transport to QQ bacteria in the CMV and thus enabled relatively long-term maintenance of cell viability. The quorum quenching effect of CMV on controlling membrane biofouling in the MBR was more pronounced with the inner flow feeding mode, which was identified by the slower increase in the trans-membrane pressure (TMP) as well as by the visual observation of a biocake that formed on the used membrane surface. In the QQ MBR with the CMV, the concentrations of extracellular polymeric substances (EPS) were substantially decreased in the biocake on the membrane surface compared with those in the conventional MBR. The CMV also showed its potential with effective biofouling control over long-term operation of the QQ MBR.
    Journal of Microbiology and Biotechnology 11/2013; 24(1). DOI:10.4014/jmb.1311.11008 · 1.53 Impact Factor
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    ABSTRACT: We propose a fused lasso logistic regression to analyze callosal thickness profiles. The fused lasso regression imposes penalties on both the l1-norm of the model coefficients and their successive differences, and finds only a small number of non-zero coefficients which are locally constant. An iterative method of solving logistic regression with fused lasso regularization is proposed to make this a practical procedure. In this study we analyzed callosal thickness profiles sampled at 100 equal intervals between the rostrum and the splenium. The method was applied to corpora callosa of elderly normal controls (NCs) and patients with very mild or mild Alzheimer's disease (AD) from the Open Access Series of Imaging Studies (OASIS) database. We found specific locations in the genu and splenium of AD patients that are proportionally thinner than those of NCs. Callosal thickness in these regions combined with the Mini Mental State Examination scores differentiated AD from NC with 84% accuracy.
    Journal of Neuroscience Methods 10/2013; 221. DOI:10.1016/j.jneumeth.2013.09.017 · 2.05 Impact Factor
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    ABSTRACT: ABSTRACT: Recently, interspecies quorum quenching by bacterial cells has been reported as a novel approach to the biofouling control in a membrane bioreactor (MBR) for wastewater treatment. In this study, a novel quorum quenching (QQ) bacterium, Pseudomonas sp. 1A1, was isolated from lab-scale MBR and was encapsulated in a microbial vessel made of a hollow fiber microporous membrane for the biofouling control in MBR. Pseudomonas sp. 1A1 was most likely to produce AHL-acylase and degraded to a wide range of N-acyl homoserine lactones (AHLs), although there was a large difference in the degradation rate of each AHL. It has an extracellular QQ activity, i.e., it produces QQ enzymes, and excretes them out of the cell. The microbial vessel encapsulating Pseudomonas sp. 1A1 was applied to a lab-scale MBR and proved substantial inhibition of the membrane biofouling.
    Industrial & Engineering Chemistry Research 01/2013; 52(31). DOI:10.1021/ie303146f · 2.59 Impact Factor
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    ABSTRACT: To compare survival in older (≥65) and younger (<65) individuals with biliary tract cancer (BTC) and to determine whether treatment efficacy varies according to age. Retrospective cohort study and nested case-control study. Tertiary referral center in Korea. Five hundred thirty-one individuals diagnosed with BTC from 2003 to 2011. Demographic and clinical characteristics of 326 older (≥65) and 205 younger (<65) individuals with BTC were compared. Differences in survival were also assessed after matching according to propensity score. There were no significant differences in sex, symptoms and signs, tumor histology, stage, or surgery between the two groups, but older participants had more comorbidities and poorer performance status and underwent less chemotherapy and radiotherapy (P < .05). Survival of the two groups was compared. After adjustment for baseline characteristics using the propensity score method, survival was still comparable (P = .72). When survival of older participants in the treatment group (TG, those who underwent surgery, chemotherapy, or radiotherapy) was compared with that of those in the supportive care group (SCG, those who received only supportive care), those in the TG had a longer survival time than those in the SCG (P < .001). This result was confirmed in the propensity analysis (including individuals undergoing surgery, P < .001; excluding individuals undergoing surgery, P < .001). In the multivariable Cox analysis, surgical resection and chemotherapy were significantly associated with longer survival, and advanced tumor stage, lower baseline serum albumin level, and greater comorbidity were found to significantly predict poor survival. Age was not associated with survival in individuals with BTC (P = .33). Older age was not associated with poor survival in BTC, and treated individuals had longer survival in the older BTC population. Therefore, treatment should not be restricted on the basis of age.
    Journal of the American Geriatrics Society 10/2012; 60(10):1862-71. DOI:10.1111/j.1532-5415.2012.04163.x · 4.57 Impact Factor
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    Sang H. Lee · Johan Lim · Erning Li · Marina Vannucci · Eva Petkova ·
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    ABSTRACT: We propose a new method to test the order between two high-dimensional mean curves. The new statistic extends the approach of Follmann (1996) to high-dimensional data by adapting the strategy of Bai and Saranadasa (1996). The proposed procedure is an alternative to the non-negative basis matrix factorization (NBMF) based test of Lee et al. (2008) for the same hypothesis, but it is much easier to implement. We derive the asymptotic mean and variance of the proposed test statistic under the null hypothesis of equal mean curves. Based on theoretical results, we put forward a permutation procedure to approximate the null distribution of the new test statistic. We compare the power of the proposed test with that of the NBMF-based test via simulations. We illustrate the approach by an application to tidal volume traces.
    Journal of Statistical Planning and Inference 09/2012; 142(9):2719–2725. DOI:10.1016/j.jspi.2012.03.001 · 0.68 Impact Factor
  • Sang H Lee · Johan Lim · Dohwan Park · Bharat B Biswal · Eva Petkova ·
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    ABSTRACT: Correctly identifying voxels or regions of interest (ROI) that actively respond to a given stimulus is often an important objective/step in many functional magnetic resonance imaging (fMRI) studies. In this article, we study a nonparametric method to detect active voxels, which makes minimal assumption about the distribution of blood oxygen level-dependent (BOLD) signals. Our proposal has several interesting features. It uses time lagged correlation to take into account the delay in response to the stimulus, due to hemodynamic variations. We introduce an input permutation method (IPM), a type of block permutation method, to approximate the null distribution of the test statistic. Also, we propose to pool the permutation-derived statistics of preselected voxels for a better approximation to the null distribution. Finally, we control multiple testing error rate using the local false discovery rate (FDR) by Efron [Correlation and large-scale simultaneous hypothesis testing. J Am Stat Assoc 102 (2007) 93-103] and Park et al. [Estimation of empirical null using a mixture of normals and its use in local false discovery rate. Comput Stat Data Anal 55 (2011) 2421-2432] to select the active voxels.
    Magnetic Resonance Imaging 07/2012; 30(10). DOI:10.1016/j.mri.2012.04.013 · 2.09 Impact Factor
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    ABSTRACT: To assess the validity of biopsy-based tests (histology, culture, and urease test) and serology in detecting current H. pylori infection for the peptic ulcer patients who had gastric bleeding. A total of 398 peptic ulcer patients were enrolled and divided into two groups, according to the presence or absence of bleeding. The diagnosis for current H. pylori infection was verified using the gold standard combining individual H. pylori tests. Sensitivity, specificity, and positive and negative predictive values of the culture, Campylobacter-like organism (CLO) test (urease test), histology, and serology were compared. Of the total study population (N = 398), 157 (39.4%) patients were categorized into the bleeding group. The sensitivities of the culture (40.0%) and CLO (85.0%) in the bleeding group were significantly lower than culture (58.1%) and CLO (96.4%) in the nonbleeding group (p = .012 and p < .001, respectively). In the bleeding group, the sensitivity of CLO (85.0%) was significantly lower than histology (92.5%) and serology (97.4%) (p = .013 and p = .002, respectively), which was not found in the nonbleeding group. The specificity of serology in the bleeding group (56.3%) was significantly lower than that of nonbleeding group (74.2%) (p = .038). Similarly, the specificity of serology was significantly lower than the other H. pylori tests in the bleeders. Bleeding decreased the sensitivity of H. pylori tests in patients with peptic ulcer, especially in urease test or culture. In contrast, histology was found to be a quite reliable test, regardless of the presence of bleeding.
    Helicobacter 04/2012; 17(2):77-85. DOI:10.1111/j.1523-5378.2011.00915.x · 4.11 Impact Factor

  • Journal of Crystal Growth 07/2011; · 1.70 Impact Factor
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    ABSTRACT: Silicon nanocoils were synthesized by annealing silicon nanowires with an outer oxide layer in reducing atmosphere. The high resolution transmission electron microscopy revealed that the reduction rate of the oxide layer was non-uniform; more precisely the cross-section of the interface of SiOx/Si was not straight but sinusoidal along the axial direction of nanowires. As a result, if the oxide layer was thicker, the diameter of the core silicon was smaller and vice versa. This non-uniformity would produce alternating tensile and compressive stresses, which were believed to cause the nanowires to get coiled.
    Journal of Crystal Growth 07/2011; 327(1):276-280. DOI:10.1016/j.jcrysgro.2011.06.018 · 1.70 Impact Factor
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    ABSTRACT: This study was designed to understand molecular and cellular mechanisms underlying aggressive behaviors in mice exposed to repeated interactions in their homecage with conspecifics. A resident-intruder procedure was employed whereby two males were allowed to interact for 10 min trials, and aggressive and/or submissive behaviors (e.g., degree of attacking, biting, chasing, grooming, rearing, or upright posture) were assessed. Following 10 days of behavioral trials, brains were removed and dissected into specific regions including the cerebellum, frontal cortex, hippocampus, midbrain, pons, and striatum. Gene expression analysis was performed using real-time quantitative polymerase-chain reaction (qPCR) for catechol-O-methyltransferase (COMT) and tyrosine hydroxylase (TH). Compared to naive control mice, significant up regulation of COMT expression of residents was observed in the cerebellum, frontal cortex, hippocampus, midbrain, and striatum; in all of these brain regions the COMT expression of residents was also significantly higher than that of intruders. The intruders also had a significant down regulation (compared to naive control mice) within the hippocampus, indicating a selective decrease in COMT expression in the hippocampus of submissive subjects. Immunoblot analysis confirmed COMT up regulation in the midbrain and hippocampus of residents and down regulation in intruders. qPCR analysis of TH expression indicated significant up regulation in the midbrain of residents and concomitant down regulation in intruders. These findings implicate regionally- and behaviorally-specific regulation of COMT and TH expression in aggressive and submissive behaviors. Additional molecular and cellular characterization of COMT, TH, and other potential targets is warranted within this animal model of aggression.
    Brain Structure and Function 04/2011; 216(4):347-56. DOI:10.1007/s00429-011-0315-z · 5.62 Impact Factor
  • Jihyun Kim · Sang H Lee · Mi R Roh ·

    The Journal of Dermatology 09/2010; 38(6):609-12. DOI:10.1111/j.1346-8138.2010.01013.x · 2.25 Impact Factor
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    ABSTRACT: We report the effect of H2 ambient annealing on the microstructure and vibrational properties of silicon nanowires (SiNWs) grown by atmospheric pressure chemical vapor depositions. The SiNWs were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Field-Emission Scanning Electron Microscopy (FESEM) and High-Resolution Transmission Electron Microscopy (HRTEM). The HRTEM study revealed that the thickness of oxide sheath surrounded by core silicon decreased with increasing H2 ambient annealing and consequently the vibrational spectra were changed. In FTIR spectra, the transverse optic and longitudinal optic peak positions of Si–O symmetry and asymmetry showed a blue shift of the outer oxide of SiNWs. The Si–O–Si peak position remained unchanged at 1080 cm−1 while the integrated absorption of Si–O–Si vibration band decreased with increasing H2 flow rate.
    Chemical Physics Letters 07/2010; 494(4-6):269-273. DOI:10.1016/j.cplett.2010.06.028 · 1.90 Impact Factor

  • Chemical Physics Letters 07/2010; · 1.90 Impact Factor
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    ABSTRACT: The eradication rate of proton-pump inhibitor-based triple therapy for Helicobacter pylori infection is low due to increasing antibiotics resistance, especially clarithromycin. Recently, it was reported in Europe that a 10-day sequential strategy produced good outcomes. The aim of this study was to assess the efficacy of sequential therapy as first-line treatment for eradication of H. pylori in clinical practice in Korea. A total of 98 patients (mean age 55.2 years and male 47, female 51) with proven H. pylori infection received 10-day sequential therapy (20 mg of rabeprazole, and 1 g of amoxicillin, twice daily for the first 5 days, followed by 20 mg of rabeprazole, 500 mg of clarithromycin, and 500 mg of metronidazole, twice daily for the remaining 5 days). Eradication was evaluated 4 weeks later, after completion of treatment by 13(C)-urea breath testing. Eradication rates were calculated by intention-to-treat (ITT) and by per protocol (PP). Compliance and adverse events were also assessed in study group. The eradication rate of sequential therapy was 91.8% (90/98) by ITT and same result was reported by PP analysis (89/97). The study group consisted of 66 H. pylori associated gastritis, 7 gastric ulcer, and 25 duodenal ulcer patients (67.3%, 7.1%, 25.5%, respectively). Mild adverse events happened frequently (21.4%) but the treatment was well tolerable. The most common adverse event was a bitter taste (9.2%) followed by nausea and diarrhea (4.1%). Ten-day sequential therapy is found to effectively eradicate H. pylori infection as first-line treatment in Korea.
    Helicobacter 04/2010; 15(2):148-53. DOI:10.1111/j.1523-5378.2010.00748.x · 4.11 Impact Factor

Publication Stats

86 Citations
44.21 Total Impact Points


  • 2011-2013
    • Nathan Kline Institute
      Orangeburg, New York, United States
  • 2010-2013
    • Seoul National University
      • • Department of Chemical and Biological Engineering
      • • Liver Research Institute
      • • Department of Materials Science and Engineering
      Sŏul, Seoul, South Korea
    • Yonsei University Hospital
      • Department of Internal Medicine
      Sŏul, Seoul, South Korea
  • 2010-2012
    • Seoul National University Bundang Hospital
      • Department of Pathology
      Sŏul, Seoul, South Korea