Myungshin Kim

Experimental investigation of the performance of R22, R407C and R410A in several capillary tubes for air-conditioners

Abstract The objective of this study is to present test results and to develop a dimensionless correlation on the basis of the experimental data of adiabatic capillary tubes for R22 and its alternatives, R407C (R32/125/134a, 23/25/52 wt.%) and R410A (R32/125, 50/50 wt.%). Several capillary tubes with different length and inner diameter were selected as test sections. Mass flow rate through the capillary tube was measured for several condensing temperatures and various degrees of subcooling at the inlet of each capillary tube. Experimental conditions for the condensing temperatures were selected as 40, 45 and 50°C, and the degrees of subcooling were adjusted to 1.5, 5 and 10°C. Mass flow rates of R407C and R410A were compared with those of R22 for the same test conditions. The results for straight capillary tubes were also compared with those of coiled capillary tubes. A new correlation based on Buckingham π theorem to predict the mass flow rate through the capillary tubes was presented based on extensive experimental data for R22, R407C and R410A. Dimensionless parameters were chosen considering the effects of tube geometry, capillary tube inlet conditions, and refrigerant properties. Dimensionless correlation predicted experimental data within relative deviations ranging from −12% to +12% for every test condition for R22, R407C and R410A. The predictions by the developed correlation were in good agreement with the results in the open literature.

Performance and heat transfer characteristics of hydrocarbon refrigerants in a heat pump system

Abstract Performance of a heat pump system using hydrocarbon refrigerants has been investigated experimentally. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane/isobutane and propane/butane are considered as working fluids in a heat pump system. The heat pump system consists of compressor, condenser, evaporator, and expansion device with auxiliary facilities such as evacuating and charging unit, the secondary heat transfer fluid circulation unit, and several measurement units. Performance of each refrigerant is compared at several compressor speeds and temperature levels of the secondary heat transfer fluid. Coefficient of performance (COP) and cooling/heating capacity of hydrocarbon refrigerants are presented. Experimental results show that some hydrocarbon refrigerants are comparable to R22. Condensation and evaporation heat transfer coefficients of selected refrigerants are obtained from overall conductance measurements for subsections of heat exchangers, and compared with those of R22. It is found that heat transfer is degraded for hydrocarbon refrigerant mixtures due to composition variation with phase change. Empirical correlations to estimate heat transfer coefficients for pure and mixed hydrocarbons are developed, and they show good agreement with experimental data. Some hydrocarbon refrigerants have better performance characteristics than R22.

Experiment and simulation on the performance of an autocascade refrigeration system using carbon dioxide as a refrigerant

The main purpose of this study is to investigate the performance of an autocascade refrigeration system using zeotropic refrigerant mixtures of R744/134a and R744/290. One of the advantages of this system is the possibility of keeping the highest pressure of the system within a limit by selecting the composition of a refrigerant mixture as compared to that in the vapor compression system using pure carbon dioxide. Performance test and simulation have been carried out for an autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Variations of mass flow rate of refrigerant, compressor power, refrigeration capacity, and coefficient of performance (COP) with respect to the mass fraction of R744 in R744/134a and R744/290 mixtures are presented at different operating conditions. Experimental results show similar trends with those from the simulation. As the composition of R744 in the refrigerant mixture increases, cooling capacity is enhanced, but COP tends to decrease while the system pressure rises.

Identification of a Stroma‐Mediated Wnt/β‐Catenin Signal Promoting Self‐Renewal of Hematopoietic Stem Cells in the Stem Cell Niche

With contrasting observations on the effects of β‐catenin on hematopoietic stem cells (HSCs), the precise role of Wnt/β‐catenin signals on HSC regulation remains unclear. Here, we show a distinct mode of Wnt/β‐catenin signal that can regulate HSCs in a stroma‐dependent manner. Stabilization of β‐catenin in the bone marrow stromal cells promoted maintenance and self‐renewal of HSCs in a contact‐dependent manner, whereas direct stabilization in hematopoietic cells caused loss of HSCs. Interestingly, canonical Wnt receptors and β‐catenin accumulation were predominantly enriched in the stromal rather than the hematopoietic compartment of bone marrows. Moreover, the active form of β‐catenin accumulated selectively in the trabecular endosteum in “Wnt 3a‐stimulated” or “irradiation‐stressed,” but not in “steady‐state” marrows. Notably, notch ligands were induced in Wnt/β‐catenin activated bone marrow stroma and downstream notch signal activation was seen in the HSCs in contact with the activated stroma. Taken together, Wnt/β‐catenin activated stroma and their cross‐talk with HSCs may function as a physiologically regulated microenvironmental cue for HSC self‐renewal in the stem cell niche. STEM CELLS 2009;27:1318–1329

Human AQP5 plays a role in the progression of chronic myelogenous leukemia (CML).

Aquaporins (AQPs) have previously been associated with increased expression in solid tumors. However, its expression in hematologic malignancies including CML has not been described yet. Here, we report the expression of AQP5 in CML cells by RT-PCR and immunohistochemistry. While normal bone marrow biopsy samples (n = 5) showed no expression of AQP5, 32% of CML patient samples (n = 41) demonstrated AQP5 expression. In addition, AQP5 expression level increased with the emergence of imatinib mesylate resistance in paired samples (p = 0.047). We have found that the overexpression of AQP5 in K562 cells resulted in increased cell proliferation. In addition, small interfering RNA (siRNA) targeting AQP5 reduced the cell proliferation rate in both K562 and LAMA84 CML cells. Moreover, by immunoblotting and flow cytometry, we show that phosphorylation of BCR-ABL1 is increased in AQP5-overexpressing CML cells and decreased in AQP5 siRNA-treated CML cells. Interestingly, caspase9 activity increased in AQP5 siRNA-treated cells. Finally, FISH showed no evidence of AQP5 gene amplification in CML from bone marrow. In summary, we report for the first time that AQP5 is overexpressed in CML cells and plays a role in promoting cell proliferation and inhibiting apoptosis. Furthermore, our findings may provide the basis for a novel CML therapy targeting AQP5.

Mesenchymal Stromal Cells Expanded in Human Allogenic Cord Blood Serum Display Higher Self-Renewal and Enhanced Osteogenic Potential

Recent clinical trials using ex vivo expanded mesenchymal stromal cells (MSCs) have raised interest in the safety and function of cultured MSCs. Here, to assess the feasibility of using allogenic human umbilical cord blood serum (CBS) for humanized clinical-grade expansion of MSCs, we characterized MSCs expanded in CBS and compared them to MSCs expanded in fetal bovine serum (FBS). MSCs in CBS exhibited a higher preservation of colony-forming cells and an accelerated expansion over serial passages with increased Oct-4 expression compared to those cultured in FBS. Notably, CBS-expanded MSCs exhibited a unique differentiation potential characterized by a shift from adipogenic to osteogenic differentiation. The differentiation shift was associated with enhanced basal and Runx2-mediated transcriptional activation of the osteocalcin promoter, as well as increased accumulation of beta-catenin and the yes-associated protein (YAP) which was independent of changes in TAZ (transcriptional co-activator with PDZ-binding motif) levels. Interestingly, the phenotypes were reversed when the FBS and CBS media were switched, suggesting the unique stimulatory effects of CBS rather than the selection of heterogeneous MSC subpopulations. The distinct regulatory effects of CBS on MSC included selective activation of platelet-derived growth factor and epidermal growth factor signals in MSCs, but not in FBS. Taken together, these results provide insight into the dynamic regulation of MSCs during ex vivo culture and show that the ex vivo culture of MSCs in allogenic human CBS provides a novel tool for the accelerated expansion of a population of MSCs that exhibit a higher self-renewal and an enhanced osteogenic potential.

3D printing technology to control BMP-2 and VEGF delivery spatially and temporally to promote large-volume bone regeneration

When large engineered tissue structures are used to achieve tissue regeneration, formation of vasculature is an essential process. We report a technique that combines 3D printing with spatial and temporal control of dual growth factors to prevascularize bone tissue. Human dental pulp stem cells (DPSCs) that have both osteogenic and vasculogenic potential were printed with bone morphogenetic protein-2 (BMP-2) in the peripheral zone of the 3D printed construct, and with the vascular endothelial growth factor (VEGF) in the central zone, in which a hypoxic area forms. The structure was implanted in the back of a mouse and tissue regeneration was assessed after 28 d. Microvessels were newly formed in the hypoxic area of the printed large volume structure, and angiogenesis from the host tissue was also observed. Bone regeneration was faster in prevascularized structures than in nonvascularized structures. The 3D-printed prevascularized structure could be a promising approach to overcome the size limitation of tissue implants and to enhance bone regeneration.

Microenvironmental Remodeling as a Parameter and Prognostic Factor of Heterogeneous Leukemogenesis in Acute Myelogenous Leukemia

Acute myelogenous leukemia (AML) is a heterogeneous disorder characterized by clonal proliferation of stem cell-like blasts in bone marrow (BM); however, their unique cellular interaction within the BM microenvironment and its functional significance remain unclear. Here, we assessed the BM microenvironment of AML patients and demonstrate that the leukemia stem cells induce a change in the transcriptional programming of the normal mesenchymal stromal cells (MSC). The modified leukemic niche alters the expressions of cross-talk molecules (i.e., CXCL12 and JAG1) in MSCs to provide a distinct cross-talk between normal and leukemia cells, selectively suppressing normal primitive hematopoietic cells while supporting leukemogenesis and chemoresistance. Of note, AML patients exhibited distinct heterogeneity in the alteration of mesenchymal stroma in BM. The distinct pattern of stromal changes in leukemic BM at initial diagnosis was associated with a heterogeneous posttreatment clinical course with respect to the maintenance of complete remission for 5 to 8 years and early or late relapse. Thus, remodeling of mesenchymal niche by leukemia cells is an intrinsic self-reinforcing process of leukemogenesis that can be a parameter for the heterogeneity in the clinical course of leukemia and hence serve as a potential prognostic factor.

Diagnostic value of AFP-L3 and PIVKA-II in hepatocellular carcinoma according to total-AFP

AIM To evaluate diagnostic value of α-fetoprotein (AFP)-L3 and prothrombin induced by vitamin K absence-II (PIVKA-II) in hepatocellular carcinoma (HCC). METHODS One hundred and sixty-eight patients during routine HCC surveillance were included in this study. Of the 168 patients, 90 (53.6%) had HCC including newly developed HCC (n = 82) or recurrent HCC after treatment (n = 8). Sera were obtained during their first evaluation for HCC development and at the time of HCC diagnosis before commencing HCC treatment. HCC was diagnosed by histological examination, appropriate imaging characteristics-computed tomography or magnetic resonance imaging. Control sera were collected from 78 patients with benign liver disease (BLD), which were obtained during routine surveillance with a suspicion of HCC. AFP, AFP-L3 and PIVKA-II were measured in the same serum by microchip capillary electrophoresis and liquid-phase binding assay on a micro-total analysis system Wako i30 auto analyzer. The performance characteristics of three tests and combined tests for the diagnosis of HCC were obtained using receiver operating characteristic curves in all populations and subgroups with AFP < 20 ng/mL. RESULTS Of 90 HCC patients, 38 (42.2%) patients had AFP < 20 ng/mL, 20 (22.2%) patients had AFP 20-200 ng/mL and 32 (35.6%) patients had AFP > 200 ng/mL. Of the 78 BLD patients, 74 (94.9%) patients had AFP < 20 ng/mL. After adjustment for age and HBV infection status, AFP-L3 levels were higher in HCC than in BLD among patients with low AFP levels (< 20 ng/mL) (P < 0.001). In a total of 168 patients, areas under the curve (AUC) for HCC were 0.879, 0.887, 0.801 and 0.939 for AFP, AFP-L3, PIVKA-II and the combined markers, respectively. The combined AUC for three markers showed higher value than the AUCs of individual marker (P < 0.05). AFP-L3 had higher AUC value than PIVKA-II for HCC detection in entire patients (P = 0.043). With combination of AFP-L3 (cut-off > 5%) and PIVKA-II (cut-off > 40 AU/L), the sensitivity were 94.4% and specificity were 75.6% in all patients. In 112 patients with low AFP levels (< 20 ng/mL), AUCs of AFP-L3, PIVKA-II and combine AFP-L3 and PIVKA-II tests were 0.824, 0.774 and 0.939, respectively. AFP-L3 with a cut-off value of 5% showed sensitivity of 71.1% and specificity of 83.8%, and PIVKA-II with a cut-off value of 40 AU/L had sensitivity of 57.9% and specificity of 95.9% in patients with low AFP levels. The combination of AFP-L3 and PIVKA-II increased the sensitivity and specificity up to 92.1% and 79.7%, respectively, in low AFP group. Combined markers detected 81.8% of early stage HCC (Union for International Cancer Control stage I), 86.7% of small sized tumor (< 2 cm) and 91.7% of single tumor of HCC in the low AFP group. In multivariate analysis, AFP-L3 was correlated with AFP and tumor size, and PIVKA-II was correlated with laboratory tests including serum aspartate aminotransferase, total bilirubin, platelets and albumin levels. PIVKA-II had no correlation with AFP, AFP-L3 or tumor characteristics. CONCLUSION Combined determination of AFP-L3 and PIVKA-II could improve the diagnostic value for HCC detection in patients with or without increased AFP levels.

Evaporation heat transfer of R-32, R-134a, R-32/134a, and R-32/125/134a inside a horizontal smooth tube

Abstract Evaporative heat transfer coefficients of R-32, R-134a, R-32/134a, and R-407C (R-32/125/134a: 23/25/52 wt%) have been measured in a horizontal smooth tube. Experiments were conducted for test section average temperatures of −12.0–17.0°C, with a mass flux of 240–1060 kg m−2 s−1, and a heat flux of 4.1–28.6 kW m−2. Evaporative heat transfer characteristics of R-407C as a possible alternative to R-22 have been compared with those of R-22. A new correlation based on superposition model for pure refrigerants and refrigerant mixtures was presented. Experimental results were compared with several correlations which predict evaporative heat transfer characteristics. Comparison with the experimental data in the open literature showed that our correlation gave a satisfactory result.