Hoon Jang

The effect of metal fibers on the friction performance of automotive brake friction materials

Abstract This study investigates the effect of different metallic fibers upon friction and wear performance of various brake friction couples. Based on a simple experimental formulation, friction materials with different metal fibers (Cu, steel, or Al) were fabricated and then evaluated using a small-scale friction tester. Two different counter disks (gray cast iron and aluminum metal matrix composite (Al-MMC)) were employed for friction tests. The friction tests were carried out at two different temperature ranges: ambient and elevated temperatures. Results from ambient temperature tests revealed that the friction materials with Cu fibers showed a pronounced negative μ – ν (friction coefficient versus sliding velocity) relation when the friction material was rubbed against gray cast iron disks, implying that stick–slip may occur at low speeds. The negative μ – ν relation was not observed when the friction material with Cu fibers was rubbed against the Al-MMC counter surface. On the other hand, elevated temperature tests showed that the friction material with Cu fibers exhibited better fade resistance than the others. The test results also showed that the friction material with steel fibers was not compatible with Al-MMC disks due to severe material transfer and erratic friction behavior during sliding at elevated temperatures.

Synergistic effects of aramid pulp and potassium titanate whiskers in the automotive friction material

Friction and wear of automotive brake friction materials were investigated using a pad-on-disk type friction tester to study the synergistic effects of aramid pulp (fibrillated organic fibers) and potassium titanate whiskers (fine ceramic whiskers). The friction materials were based on a simple formulation with five ingredients (phenolic resin, aramid pulp, potassium titanate whiskers, molybdenum disulfide, and barite). Friction stability, wear rate, and morphology of sliding surfaces were carefully examined to investigate the effect of the two different fibrous ingredients in the friction material on various friction properties. The results showed that both aramid pulp and potassium titanate whiskers played a crucial role for the friction characteristics by maintaining the durable friction film on the rubbing surface. The friction film provided improved friction stability and wear resistance. Microscopic observations of the friction material exhibited that the fine ceramic whiskers adhered to the fibrillated aramid fibers, providing heat resistance and strength to the friction film at the rubbing interface. The beneficial synergistic effect from the two fibrous ingredients, however, was significantly diminished when only one of them was employed.

Compositional effects of the brake friction material on creep groan phenomena

Abstract Creep groan (low frequency frictional vibration in the range of 200–500xa0Hz during braking at a very low vehicle speed) was studied by changing the relative amounts of ingredients in a brake friction material containing 12 ingredients. Twenty-nine friction material specimens with different relative amounts of the ingredients were manufactured according to a constrained mixture design. The difference (Δ μ ) between kinetic ( μ k ) and static ( μ s ) coefficients of friction for each formulation was measured to investigate creep groan propensity of each friction material since the creep groan is caused by stick–slip phenomena. Results showed that zircon (zirconium silicate), steel wool, and phenolic resin showed a tendency to increase Δ μ . On the other hand, antimony trisulfide, cashew particles, and rockwool tended to reduce Δ μ . Based on the results of this work, the initial formulation was modified to reduce Δ μ . The modified friction material showed a smaller Δ μ value than the initial friction material implying low propensity of creep groan phenomena during braking. The velocity dependence of the friction coefficient was also examined using the initial and the modified friction materials. The modified formulation exhibited a less negative μ – V relation than the initial formulation.

Tribological study of gray cast iron with automotive brake linings: The effect of rotor microstructure

Experimental studies of friction characteristics were conducted using gray cast iron and automotive brake linings. The gray iron samples were manufactured to have different microstructures by changing the carbon equivalent and cooling speeds of melts and two different types of non-commercial brake linings (non-steel and steel-containing linings) were used as a counter material. Friction tests were performed on a pad-on-disk type tribotester and particular emphases were given to the effect of graphite flakes and ferrite in the gray iron disks on fade phenomena and the level of the coefficient of friction. Results showed that the coefficient of friction increased with the amount of graphite flakes on the gray iron and the effect was more pronounced in the case of using steel-containing linings. The amount of ferrite phase on the disk surface showed little influence on the coefficient of friction. Fade resistance of non-steel linings was improved with the increase of graphite flakes on the disk surface and steel-containing linings showed good fade resistance regardless of graphite contents in the gray iron disks.

‘Shotgun DNA synthesis’ for the high-throughput construction of large DNA molecules

We developed a highly scalable ‘shotgun’ DNA synthesis technology by utilizing microchip oligonucleotides, shotgun assembly and next-generation sequencing technology. A pool of microchip oligonucleotides targeting a penicillin biosynthetic gene cluster were assembled into numerous random fragments, and tagged with 20u2009bp degenerate barcode primer pairs. An optimal set of error-free fragments were identified by high-throughput DNA sequencing, selectively amplified using the barcode sequences, and successfully assembled into the target gene cluster.

Melatonin prevents cisplatin-induced primordial follicle loss via suppression of PTEN/AKT/FOXO3a pathway activation in the mouse ovary

Premature ovarian failure (POF) is a major side effect of chemotherapy in young cancer patients. To develop pharmaceutical agents for preserving fertility, it is necessary to understand the mechanisms responsible for chemotherapy‐induced follicle loss. Here, we show that treatment with cisplatin, a widely used anticancer drug, depleted the dormant follicle pool in mouse ovaries by excessive activation of the primordial follicles, without inducing follicular apoptosis. Moreover, we show that co‐treatment with the antioxidant melatonin prevented cisplatin‐induced disruption of the follicle reserve. We quantified the various stages of growing follicles, including primordial, primary, secondary, and antral, to demonstrate that cisplatin treatment alone significantly decreased, whereas melatonin co‐treatment preserved, the number of primordial follicles in the ovary. Importantly, analysis of the PTEN/AKT/FOXO3a pathway demonstrated that melatonin significantly decreased the cisplatin‐mediated inhibitory phosphorylation of PTEN, a key negative regulator of dormant follicle activation. Moreover, melatonin prevented the cisplatin‐induced activating phosphorylation of AKT, GSK3β, and FOXO3a, all of which trigger follicle activation. Additionally, we show that melatonin inhibited the cisplatin‐induced inhibitory phosphorylation and nuclear export of FOXO3a, which is required in the nucleus to maintain dormancy of the primordial follicles. These findings demonstrate that melatonin attenuates cisplatin‐induced follicle loss by preventing the phosphorylation of PTEN/AKT/FOXO3a pathway members; thus, melatonin is a potential therapeutic agent for ovarian protection and fertility preservation during chemotherapy in female cancer patients.

Initial Experience of Robot-Assisted Radical Cystectomy with Total Intracorporeal Urinary Diversion: Comparison with Extracorporeal Method

PURPOSEnTo report our surgical technique and initial experience with robot-assisted laparoscopic radical cystectomy (RARC) with total intracorporeal urinary diversion compared with an extracorporeal method.nnnSUBJECTS AND METHODSnIn total, 42 patients underwent RARC by a single surgeon at our institute for clinically localized bladder cancer. Among these, 4 patients underwent RARC with complete intracorporeal urinary diversion. An ileal conduit was achieved in 3 patients, and an orthotopic neobladder was created in 1 patient. Our surgical technique is presented in detail, and the intracorporeal cases were compared with 38 previous extracorporeal diversion cases for perioperative outcome, postoperative oncologic outcome, and complications.nnnRESULTSnThree men and 1 woman underwent complete intracorporeal urinary diversion. In patients receiving ileal conduits the mean total operative time was 510 minutes, and the estimated blood loss was 400 mL. In the patient receiving an ileal neobladder the total operative time was 585 minutes, and the estimated blood loss was 500 mL. Mean time to flatus was 60 hours, and no intraoperative or postoperative major complications occurred. Surgical margins were negative with no positive lymph nodes. Compared with extracorporeal cases, the mean total operative time for RARC was significantly longer, but perioperative outcomes of estimated blood loss, time to flatus, and postoperative oncologic outcomes were not significantly different.nnnCONCLUSIONSnOur initial experience showed that RARC with complete intracorporeal urinary diversion is feasible based on perioperative data and oncologic features. However, in this small case series, we observed no definite benefits associated with intracorporeal urinary diversion over extracorporeal urinary diversion except for better cosmesis. Long-term, large-scale, prospective comparative studies will be needed to demonstrate the benefit of intracorporeal urinary diversion.

Identification of somatic mutations in EGFR

BackgroundLung adenocarcinoma is a highly heterogeneous disease with various etiologies, prognoses, and responses to therapy. Although genome-scale characterization of lung adenocarcinoma has been performed, a comprehensive somatic mutation analysis of EGFR/KRAS/ALK-negative lung adenocarcinoma in never-smokers has not been conducted.MethodsWe analyzed whole exome sequencing data from 16 EGFR/KRAS/ALK-negative lung adenocarcinomas and additional 54 tumors in two expansion cohort sets. Candidate loci were validated by target capture and Sanger sequencing. Gene set analysis was performed using Ingenuity Pathway Analysis.ResultsWe identified 27 genes potentially implicated in the pathogenesis of lung adenocarcinoma. These included targetable genes involved in PI3K/mTOR signaling (TSC1, PIK3CA, AKT2) and receptor tyrosine kinase signaling (ERBB4) and genes not previously highlighted in lung adenocarcinomas, such as SETD2 and PBRM1 (chromatin remodeling), CHEK2 and CDC27 (cell cycle), CUL3 and SOD2 (oxidative stress), and CSMD3 and TFG (immune response). In the expansion cohort (Nu2009=u200970), TP53 was the most frequently altered gene (11%), followed by SETD2 (6%), CSMD3 (6%), ERBB2 (6%), and CDH10 (4%). In pathway analysis, the majority of altered genes were involved in cell cycle/DNA repair (P <0.001) and cAMP-dependent protein kinase signaling (P <0.001).ConclusionsThe genomic makeup of EGFR/KRAS/ALK-negative lung adenocarcinomas in never-smokers is remarkably diverse. Genes involved in cell cycle regulation/DNA repair are implicated in tumorigenesis and represent potential therapeutic targets.

Oncologic and Functional Outcomes after Partial Nephrectomy Versus Radical Nephrectomy in T1b Renal Cell Carcinoma: A Multicenter, Matched Case-Control Study in Korean Patients

Purpose The study was to compare the oncologic and functional outcomes of partial nephrectomy (PN) and radical nephrectomy (RN) for pathologically proven T1b renal cell carcinoma using pair-matched groups. Materials and Methods We reviewed our prospectively maintained database for RN and PN in T1b renal tumors surgically treated between 1999 and 2011 at five institutions in Korea. Of 611 patients treated with PN or RN for a solitary and NX/N0 M0 renal mass (4-7 cm), 577 (PN, 100; RN, 477) patients with pathologically confirmed pT1b remained for analysis. Study subjects were grouped by PN or RN, then matched by age, sex, comorbidities, body mass index, tumor size and depth, histologic type, and preoperative estimated glomerular filtration rate (eGFR) using propensities score. To evaluate oncologic outcomes, overall survival (OS), cancer-specific survival (CSS), and progression-free survival (PFS) rates were analyzed. The functional outcomes were evaluated by postoperative eGFR. Results The median follow-up in the RN group was 48.1 and 42.6 months in the PN group. The estimated 10-year CSS rate (PN 85.7% vs. RN 84.4%, p=0.52) and 5- and estimated 10-year PFS rates (PN: 86.4% and 79.2% vs. RN: 86.0% and 66.1%, p=0.66) did not differ significantly between groups. The estimated 10-year OS rate was significantly higher in the PN group (85.7%) compared to the RN group (73.3%) (p=0.003). PN was less likely to induce new-onset chronic kidney disease (CKD) and end-stage CKD compared with RN. Conclusion Our study suggests that patients treated with PN demonstrate a superior OS rate and postoperative renal function with analogous CSS and PFS rates compared with pair-matched patients treated with RN.

Identification of somatic mutations in EGFR / KRAS / ALK -negative lung adenocarcinoma in never-smokers

BackgroundLung adenocarcinoma is a highly heterogeneous disease with various etiologies, prognoses, and responses to therapy. Although genome-scale characterization of lung adenocarcinoma has been performed, a comprehensive somatic mutation analysis of EGFR/KRAS/ALK-negative lung adenocarcinoma in never-smokers has not been conducted.MethodsWe analyzed whole exome sequencing data from 16 EGFR/KRAS/ALK-negative lung adenocarcinomas and additional 54 tumors in two expansion cohort sets. Candidate loci were validated by target capture and Sanger sequencing. Gene set analysis was performed using Ingenuity Pathway Analysis.ResultsWe identified 27 genes potentially implicated in the pathogenesis of lung adenocarcinoma. These included targetable genes involved in PI3K/mTOR signaling (TSC1, PIK3CA, AKT2) and receptor tyrosine kinase signaling (ERBB4) and genes not previously highlighted in lung adenocarcinomas, such as SETD2 and PBRM1 (chromatin remodeling), CHEK2 and CDC27 (cell cycle), CUL3 and SOD2 (oxidative stress), and CSMD3 and TFG (immune response). In the expansion cohort (Nu2009=u200970), TP53 was the most frequently altered gene (11%), followed by SETD2 (6%), CSMD3 (6%), ERBB2 (6%), and CDH10 (4%). In pathway analysis, the majority of altered genes were involved in cell cycle/DNA repair (P <0.001) and cAMP-dependent protein kinase signaling (P <0.001).ConclusionsThe genomic makeup of EGFR/KRAS/ALK-negative lung adenocarcinomas in never-smokers is remarkably diverse. Genes involved in cell cycle regulation/DNA repair are implicated in tumorigenesis and represent potential therapeutic targets.