95 research outputs found
High methane selective Pt cluster catalyst supported on Ga2O3 for CO2 hydrogenation
No full textIn heterogeneous catalysis, the CO2 hydrogenation reaction is an important class of reactions that has been widely studied for decades. Particularly, the particle size of the metal plays a crucial role in controlling the selectivity of the CO2 hydrogenation reaction. However, there have only been a few studies investigating the selectivity for sub-nanometer sized particles. Here, we report the effect of Pt particle size on the catalytic activity and selectivity of CO2 hydrogenation. The size of the Pt particles was tuned by changing the amount of loading. With low Pt loading on gallium oxide, Pt clusters were formed; however, Pt nanoparticles were synthesized with high Pt loading. The Pt clusters were mainly edge and step sites where CO2 adsorbs more strongly, while the Pt nanoparticles were mainly composed of terrace sites. The catalytic performance of the Pt catalysts was examined using CO2 hydrogenation. The Pt clusters showed a higher methane selectivity than that of the Pt nanoparticles. The reaction mechanism was analyzed by diffuse reflectance infrared fourier transform (DRIFT) spectroscopy at reaction conditions. The Pt clusters mainly showed the formate peak, while showing fewer carbonate peaks than the support. These results suggest that the formation of CH4 follows the formate route11Nsciescopu
Phloretin inhibits the human prostate cancer cells through the generation of reactive oxygen species
No full textPhloretin is a flavonoid with known anticancer activities. However, we do not fully understand how phloretin mitigates prostate cancer on the molecular level. In the present study, we examined changes in proliferation, colony formation, and migration after phloretin treatment in human prostate cancer cells PC3 and DU145. We measured reactive oxygen species (ROS) and gene expression. Phloretin increased ROS and suppressed cell proliferation, migration, and colony formation in both cell lines. Additionally, phloretin treatment increased oxidative stress, as demonstrated through lower antioxidant enzymes (catalase, SOD2, Gpx1, Gpx3). In addition, their regulator CISD2 decreased in expression. We also found that increased ROS significantly downregulated multiple components of the Wnt/β-catenin signaling pathway (β-catenin, TCF4, FoxA2, c-Myc) and Twist1. Thus, anticancer activity of phloretin against human prostate cancer cells occurs through generating ROS to influence Wnt/β-catenin signaling. The results of this study suggest that phloretin has a therapeutic effect on prostate cancer in vitro, inhibiting the proliferation and migration of cancer cell lines PC3 and DU145. The mechanism of phloretin appears to be increasing ROS production. We thus recommend phloretin as a promising anticancer therapeutic agent.
Oxygen activation on the interface between Pt nanoparticles and mesoporous defective TiO2 during CO oxidation
No full text© 2019 Author(s).Platinum-based heterogeneous catalysts are mostly used in various commercial chemical processes because of their high catalytic activity, influenced by the metal/oxide interaction. To design rational catalysts with high performance, it is crucial to understand the relationship between the metal-oxide interface and the reaction pathway. Here, we investigate the role of oxygen defect sites in the reaction mechanism for CO oxidation using Pt nanoparticles supported on mesoporous TiO2 catalysts with oxygen defects. We show an intrinsic correlation between the catalytic reactivity and the local properties of titania with oxygen defects (i.e., Ti3+ sites). In situ infrared spectroscopy observations of the Pt/mesoporous TiO2-x catalyst indicate that an oxygen molecule bond can be activated at the perimeter between the Pt and an oxygen vacancy in TiO2 by neighboring CO molecules on the Pt surface before CO oxidation begins. The proposed reaction pathways for O2 activation at the Pt/TiO2-x interface based on density functional theory confirm our experimental findings. We suggest that this provides valuable insight into the intrinsic origin of the metal/support interaction influenced by the presence of oxygen vacancies, which clarifies the pivotal role played by the support11sciescopu
Influence of Support Acidity of Pt/Nb 2 O 5 Catalysts on Selectivity of CO 2 Hydrogenation
No full text© 2019, Springer Science+Business Media, LLC, part of Springer Nature. Abstract: In solid acid catalysis, understanding the impact of support acidity on catalytic performance has remained a controversial issue. The selected catalytic systems often rely on mixing different substances to control the degree of acidity, which in turn, also modifies other parameters in the system, making it challenging to perform a definitive study. To specifically investigate the role of support acidity, we performed a systematic study employing Nb 2 O 5 as the catalyst support, which acidity can be controlled by calcination. The catalytic behavior of the fabricated Pt/Nb 2 O 5 catalysts was evaluated using CO 2 hydrogenation to methanol (MeOH) and dimethyl ether (DME). An increase in the acidity of the support resulted in an improvement in the CO 2 conversion owing to the strong interaction between the Pt and the catalyst support, but it was detrimental for the production of MeOH because of the unfavorable adsorption of CO 2 molecules and the formation of carbon-containing species on the surface of the support with high acidity. DME selectivity was enhanced with an increase in catalyst acidity, confirming the role of solid acids for the production of DME from CO 2 reduction. Graphical Abstract: By controlling the calcination temperature of Nb 2 O 5 , tunable support acidity was obtained. CO 2 conversion increased while the selectivity of methanol and dimethyl ether decreased with increasing support acidity.11sciescopu
TouchPhoto: Enabling Independent Picture Taking and Understanding for Visually-Impaired Users
No full textThis paper presents TouchPhoto, which provides visualaudio- tactile assistive features to enable visually-impaired users to take and understand photographs independently. A user can take photographs under auditory guidance and record audio tags to aid later recall of the photographs' contents. For comprehension, the user can listen to audio tags embedded in a photograph while touching salient features, e.g., human faces, using an electrovibration display. We conducted two user studies with visually-impaired users, one for picture taking and the other for understanding and recall, in a two-month interval. They considered auditory assistance as very useful for taking and understanding photographs and tactile features as helpful but to a limited extent. © 2019 Copyright held by the owner/author(s).1
Size-controlled model Ni catalysts on Ga2O3 for CO2 hydrogenation to methanol
No full text© 2019 Elsevier Inc.The effect of particle size for Ni nanoparticles supported on β-Ga2O3 was investigated for CO2 hydrogenation to methanol at 0.5 MPa. Model Ni nanoparticles ranging from 3.3 to 10.2 nm were synthesized using the hot injection method by controlling the reaction temperature and time. The smallest Ni nanoparticles (3.3 nm) showed the highest catalytic activity across the entire temperature range and the largest Ni nanoparticles (10.2 nm) showed the highest methanol selectivity. The apparent activation energies for methanol with Ni nanoparticles increased from 6.0 to 18.4 kcal mol−1 as the nanoparticle size increased. Furthermore, it was found that the smallest Ni nanoparticles favor the reverse water gas shift reaction. In situ DRIFT analysis revealed that the gallium oxide itself could produce an intermediate species and the addition of Ni on the oxide support increases the hydrogenation rate. The Ni supported catalysts showed a CO peak, but the smallest Ni nanoparticles showed a larger CO peak than that for the largest Ni nanoparticles, which clearly supports that the smaller nanoparticles favor the reverse water gas shift reactio
Defective Nb2O5-supported Pt catalysts for CO oxidation: Promoting catalytic activity via oxygen vacancy engineering
No full text© 2019 Elsevier Inc.We introduced oxygen vacancies into Nb2O5 via thermal treatment at 700 °C under oxygen-deficient conditions for different lengths of time. Niobia-supported Pt catalysts were subsequently synthesized using the wet impregnation method with the fabricated Nb2O5. The catalytic activity of the synthesized catalysts for CO oxidation exhibited a significant increase from that obtained for a counterpart having the Nb2O5 support treated under saturated oxygen conditions (i.e., in air). Moreover, increasing the number of oxygen vacancies was found to increase the catalytic activity. At 150 °C, the TOF calculated for the catalyst with the most oxygen vacancies was 0.36 s−1, which was much higher than that obtained from the catalyst possessing the fewest oxygen vacancies (0.05 s−1). Systematic characterization of the synthesized catalysts revealed the crucial impact of oxygen vacancies and active lattice oxygen on the enhancement of catalytic activit
Coordinated neurostimulation promotes circuit rewiring and unlocks recovery after spinal cord injury
No full textFunctional recovery after incomplete spinal cord injury depends on the effective rewiring of neuronal circuits. Here, we show that selective chemogenetic activation of either corticospinal projection neurons or intraspinal relay neurons alone led to anatomically restricted plasticity and little functional recovery. In contrast, coordinated stimulation of both supraspinal centers and spinal relay stations resulted in marked and circuit-specific enhancement of neuronal rewiring, shortened EMG latencies, and improved locomotor recovery. Functional recovery after spinal cord injury is guided by the formation of new spinal detour circuits. The authors show that the formation of these circuits is enhanced by targeted chemogenetic stimulation of supraspinal and spinal neuron populations. Supraspinal and spinal coordinated stimulation potentiated behavioral recovery
인간화마우스 모델을 활용한 Francisella tularensis 항원의 면역반응에 관한 연구
No full text학위논문 (박사)-- 서울대학교 대학원 : 수의과대학 수의학과, 2018. 8. 박재학.Francisella tularensis (FT), a highly infectious pathogen, is considered to be a potential biological weapon because of its low infectious dose, and the ability of aerosol transmission. Although an attenuated FT live vaccine strain (LVS) has been developed, this vaccine exhibits side effects and residual virulence. Therefore, subunit vaccines using parts of pathogens have been proposed as an alternative to live vaccines. Tul4 and FopA are outer membrane proteins of FT, and have been reported to play an important role in the bacteriums immunogenicity, which support the potential of subunit vaccines as candidates against FT.
Although in vitro and mouse models are standard paradigms for vaccine development, these models have limitations including differences in susceptibility to FT between mice and humans. Humanized mice (hu-mice) bearing the human immune system have been developed to study human-specific diseases, and have been reported to produce human immunoglobulins against pathogens. Therefore, hu-mice have the potential to overcome the limitations of animal models used in clinical research. In this study, we reported that a subunit vaccine constructed based upon outer membrane epitopes, Tul4 and FopA, elicited the human-specific immunity in hu-mice model.
The study described in Chapter I reported the in vitro and in vivo immune response of a subunit vaccine comprising the recombinant peptides Tul4 and FopA generated from epitopes on FT outer membrane proteins. Dendritic cells (DCs) stimulated by recombinant peptides with adjuvant CpG oligodeoxynucleotide induced robust immunophenotypic changes in DC maturation and secretion of inflammatory cytokines (interleukin [IL]-6 and IL-12). In addition, the matured DCs enabled ex vivo proliferation of naive splenocytes in mixed lymphocyte reactions. Finally, I investigated in vivo immune responses by assessing antibody production in C57BL/6 mice. Total immunoglobulin (Ig) G was produced after immunization and levels peaked 6 weeks later. Moreover, Tul4-specific IgG was confirmed in mice receiving peptides with or without CpG. Based on these results, I revealed that the recombinant peptides Tul4 and FopA have immunogenicity, and could be a safe subunit vaccine candidate against FT.
Chapter II described the immune response of mice—humanized with human CD34+ cells (hu-mice)—to a cocktail of recombinant Tul4 and FopA (rTul4 and rFopA), which were codon-optimized and expressed in Escherichia coli. Not only did the cocktail-immunized hu-mice produce a significant human immunoglobulin response, they also exhibited prolonged survival against an LVS, as well as human T cells in the spleen. These results suggest that a cocktail of rTul4 and rFopA had successfully induced an immune response in the hu-mice, demonstrating the potential of this mouse model for use in the evaluation of FT vaccine candidates.
In conclusion, the present study demonstrates the efficacy of recombinant Tul4 and FopA vaccine and the value of the hu-mice model for FT vaccine research. Overall, I suggest that such an approach might be widely applicable to vaccine studies of the FT.ABSTRACT i
TABLE OF CONTENTS iv
LIST OF FIGURES viii
LIST OF TABLES x
LIST OF ABBREVIATION xi
GENERAL INTRODUCTION xiii
LITERATURE REVIEW xvi
CHAPTER I Synthetic Tul4 and FopA peptides cocktail of Francisella tularensis induced humoral and cell-mediated immunity in mice 1
1 INTRODUCTION 2
2 MATERIALS AND METHODS 4
2.1 Mice 4
2.2 Synthetic peptides and adjuvant preparation 4
2.3 Generation of bone marrow derived dendritic cells 4
2.4 In vitro DC stimulation assay 5
2.5 Mixed lymphocyte reaction (MLR) 6
2.6 Immunizations with peptides 6
2.7 Ex vivo spleen re-stimulation 6
2.8 Humoral and cellular immune response of the mice 7
2.9 Statistical analysis 8
3 RESULTS 9
3.1 Synthetic peptides-stimulated maturation of BMDCs 9
3.2 Allostimulatory function of BMDCs pulsed with synthetic peptides 11
3.3 Immune response of splenocytes in mice immunized with synthetic peptides 13
3.4 Antibody response in mice immunized with synthetic peptides 15
4 DISCUSSION 18
CHAPTER II Humanized mice for the evaluation of Francisella tularensis vaccine candidates 22
1 INTRODUCTION 23
2 MATERIALS AND METHODS 25
2.1 Production of recombinant Tul4 and FopA proteins 25
2.2 Mice 25
2.3 Establishment of humanized mice 26
2.4 Analysis of human cell engraftment 26
2.5 Vaccination of the humanized mice 26
2.6 Humoral immune response 27
2.7 Challenge test 28
2.8 Histopathological analysis 28
2.9 Statistical analysis 31
3 RESULTS 32
3.1 Cloning, expression, and purification of the rTul4 and rFopA 32
3.2 Human specific immune response after immunization in humanized mice 34
3.3 Partial protection against LVS in humanized mice immunized with rTul4 and rFopA 38
4 DISCUSSION 46
GENERAL CONCLUSION 49
REFERENCES 52
국문초록 73
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Temperature Measurement of Carbon Dioxide Using Emission Spectroscopy
No full textThis paper presents a relatively simple method for temperature measurement of hot carbon dioxide gas using an emission spectroscopy setup. The v3 band emission at 4.3 um is detected using an optical bandpass filter and a mercury cadmium telluride detector. A conversion methodology is introduced that calculates the detector voltage from the spectral radiance considering the spectral sensitivities of the optical components and the non-linear characteristics of the detector. Two radiation models, a line-by-line model and a random statistical narrow band model, are employed to calculate the spectral radiance at given flow conditions. Black body radiation is considered for radiance calculation for optically thick conditions. Temperatures under test conditions in a shock tube are determined using the proposed conversion methodology and are compared with the temperatures obtained from a computational fluid dynamics simulation. The accuracy and efficiency of the temperature measurement using the two radiation models and the black body curve are compared. It is confirmed that the proposed method is a reliable way to determine the temperature while using a relatively simple experimental setup. Detector voltages are presented for a wide range of temperature, pressure, and beam path length for applications under different test conditions.
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