Do audit fees and audit hours influence credit ratings?: A comparative analysis of Big4 vs Non-Big4

We examine the relationship between credit ratings / changes and audit fees (hours) for Big4 and Non-Big4 firms. Audit fee (hours) may be considered as a default risk metric for credit ratings agencies. However, firms audited by Big4 are larger, better performing and operate with lower leverage compared to firms followed by Non-Big4. Therefore, the association between audit fee (hours) may be different for firms followed by Big4 and Non-Big4 audit firms. We find that there is a negative association between audit fees and credit ratings for firms followed by Big4 audit firms. However, we find an insignificant relation for firms followed by Non-Big4. We conjecture the different association due to the Big4 firms having more robust accounting procedures; Big4 firms must offer competitive audit fees because they are engaged in fierce competition with other Big4 firms. Moreover, Big4 and Non-Big4 firms have different relationships with their clients because Non-Big4 firms are more income dependent on their clients. Using a sample of 1,717 firm–year observations between 2002 and 2013, we establish a relation between audit fees in period t and credit ratings in period t+1, for firms followed by Big4 auditors. We do not find a significant relation for firms followed by Non-Nig4 firms, suggesting that credit ratings agencies perceive audit fee differently for Big4 and Non-Big4 firms. Client firms followed by Big4 auditors that experience a credit rating change in period t+1 pay lower audit fees in period t compared to firms that do not experience a credit rating change. Our additional analysis suggests a different association between firms audit fees and firm performance for firms that experience a credit rating increase and decrease. Firms that experience a credit ratings increase in period t+1 have strong performance and lower audit fees in period t. On the other hand, firms that experience a credit rating decrease have weak financial performance and negative audit fees compared to firms that do not experience a credit ratings change. Our results suggest that audit fees combined with financial performance influence a credit ratings agency' perception of default risk

멀티미디어 프로세서의 ASIC 구현

학위논문(석사)--서울대학교 대학원 :전기.컴퓨터공학부,2001.Maste

건식숙성 소고기 크러스트의 항산화 및 ACE 저해활성과 패티 제조시 풍미증진제로서의 활용

학위논문 (석사)-- 서울대학교 대학원 : 농업생명과학대학 농생명공학부, 2018. 8. 조철훈.The objective of present experiments was 1) to determine the antioxidant and angiotensin I–converting enzyme (ACE) inhibitory activity of the crust of dry-aged beef, and 2) to find the way of utilizing the crust as a flavor enhancer in the manufacturing beef patty. Experiment I. Evaluation of antioxidant and ACE inhibitory activity of crust derived from dry aged beef Moisture evaporation of meat surface in dry aging process inevitably produces crust which is cut and discarded before consumption. Antioxidant activity, ACE inhibitory activity, and protein profile of the crust were evaluated compared with un-aged, wet-, and dry-aged beef. The antioxidant activity was determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-di-(3-ethylbenzthiazoline sulphonate) (ABTS) radical scavenging, ferric reducing antioxidant power (FRAP), and ferrous ion chelating activity. The crust samples showed the greatest (P<0.05) antioxidant activity resulting from the 3 different mechanisms of action (radical scavenging, non-radical redox potential activity, and metal cheating) as antioxidant and ACE inhibitory activity among the treatment. Protein bands with small molecular weight indicating potent bioactivity were appeared in myofibrillar protein profile of the crust sample. The lowest (P<0.05) ACE inhibitory activity was observed in un-aged beef. Based on results from this study, it could be suggested the crust, usually recognized as discarded portion of dry-aged beef, can be utilized in various areas as functional ingredient possessed antioxidant and ACE inhibitory activity. Experiment II. Application of the crust from dry-aged beef on beef patty and its quality assessment The aim of this study was to find the way of utilizing the crust in meat products to enhance sensory characteristic and to reduce expensive waste. Total of four sirloins were dry-aged for 28 days at 4°C (75% relative humidity). The crust was obtained from surface of the dry-aged beef and prepared as powdered form after freeze-drying. Patties were prepared with 75% ground beef, 20% beef fat, 0.3% salt, and the crust [0 (control) and 5%w/w] The patties were packaged with aerobic method and stored at 4°C for 4 or 6 days with 2-day interval, respectively. The patties with the crust showed higher score in flavor, tenderness, and acceptability by sensory panel compared to control. In addition, different profile was observed in electronic nose analysis between with and without crust group. In conclusion, the crust from dry-aged beef could be used as flavor enhancer in meat products by providing beefy and palatable flavor without long period of dry aging time as meat industry practiced commonly.Chapter I. General Introduction 1 Chapter II. Evaluation of antioxidant and ACE inhibitory activity of crust derived from dry aged beef 6 2.1. Introduction 6 2.2. Materials and Methods 7 2.2.1. Meat Sample preparation 7 2.2.2. Extraction 8 2.2.3. Antioxidant activity 8 2.2.3.1. DPPH assay 9 2.2.3.2. ABTS assay 9 2.2.3.3. FRAP assay 10 2.2.3.4. Ferrous ion chelating activity assay 10 2.2.4. ACE inhibitory activity 11 2.2.5. SDS-Page 12 2.2.6. Statistical analysis 13 2.3. Results and Discussion 14 2.3.1. Antioxidant activity of meat extracts obtained from four different beef samples 14 2.3.1.1. Radical scavenging activity 14 2.3.1.2. Ferric ions reducing power 17 2.3.1.3. Metal chelating activity 17 2.3.2. ACE inhibitory activity 18 2.3.3. Protein profile using SDS-PAGE 20 2.4. Conclusion 21 References 22 Chapter III. Application of the crust from dry-aged beef on beef patty and its quality assessment 26 3.1. Introduction 26 3.2. Materials and Methods 28 3.2.1. Preparation of patties 28 3.2.2. Sensory evaluation 29 3.2.3. Electronic nose 29 3.2.4. Texture analysis 30 3.2.5. Total aerobic bacterial counts 30 3.2.6. Lipid oxidation 31 3.2.7. Statistical analysis 32 3.3. Results and Discussion 33 3.3.1. Sensory evaluation and electronic nose 33 3.3.2. Texture analysis 36 3.3.3. Total aerobic bacterial counts 38 3.3.4. Lipid oxidation 40 3.4. Conclusion 42 References 43 Chapter IV. Overall Conclusion 48 Summary in Korean 49 Acknowledgement 51Maste

NURBS 자유 곡면을 이용한 의료 모델 변경 시스템 개발에 관한 연구

Thesis (master`s)--서울대학교 대학원 :산업공학과,2001.Maste

Low-power Temperature Sensor

MasterThis thesis describes a design of an ultra-low power temperature sensor suitable for wearable sensor interface. A low power bandgap reference generator circuit is combined with a 10b successive approximation register based analog-to-digital converter. The temperature sensor, designed with 0.35um technology, shows a resolution of 0.164℃ in a conversion range of 0℃ to 100℃. With a conversion time of 60μs, the sensor consumes only 11.7nW from single 1.3V supply voltage at room temperature.본 논문에서는 낮은 전력을 소비하여 높은 정확도를 가지고 온도를 측정하기 위한 Temperature Sensor를 설계하였다. 제안된 temperature sensor는 Bandgap Reference 생성 회로를 변형하여 온도와 비례하거나 반비례한 전압을 따로 분리하고 각 전압을 ADC로 연결하여 디지털 값으로 변환하는 방법으로 온도를 측정한다. 기존의 Bandgap reference 생성 회로에서는 온도에 정비례하는 PTAT 전압과 반비례하는 CTAT 전압을 합하여 reference 전압을 생성하였다. 이러한 회로를 변형하여 PTAT 전압과 CTAT 전압을 따로 분리하였다. PTAT 전압은 두 개의 diode를 거꾸로 연결하여 위쪽 diode의 saturation 전류를 이용하였는데 이 경우 saturation 전류를 사용하기 때문에 전류의 크기가 매우 작아 전력 소비 또한 작게 할 수 있다. CTAT 전압은 diode를 정방향으로 연결하고 전류를 거의 일정하게 유지시켜서 얻었다. ADC는 SAR 타입의 ADC를 사용을 하였다. SAR 타입은 전력 소비를 최소로 하고자 할 때 알맞은 ADC이다. BGVR회로에서 생성한 PTAT와 CTAT전압을 ADC의 두 차동 입력으로 연결하였다. ADC내의 comparator는 차동 전압의 차이를 시간 domain으로 옮겨와 두 신호의 전파 속도 차이로 비교를 진행한다. 이러한 방식의 comparator는 공급 전압이 낮을수록 동작이 잘 된다는 장점이 있다. 설계된 Temperature sensor의 총 소비 전력은 11.7nW였으며, conversion time은 60μs로 측정이 되었다. 이는 현존하는 온도 센서 중 가장 낮은 값을 나타낸다. 앞으로 최소의 전력을 소모하여 정밀하게 온도를 측정할 수 있는 큰 발판을 마련할 수 있는 것으로 생각된

누설 전류를 이용한 초저전력 온도 센서 연구

DoctorThe performance of critical building blocks for ultra-low-power (ULP) applications often causes strong temperature dependencies. Since the temperature sensitivities need to be compensated, an on-chip temperature sensor is becoming one of the essential blocks in ULP system-on-chips (SoC). This thesis presents temperature sensors with a leakage-based bandgap-Vth reference. The first temperature sensor combines a leakage-based bandgap-Vth reference and an asynchronous SAR ADC. By sampling leakage-based biases directly by the SAR ADC, the sensor consumes 490pW at 20ºC with a conversion time of 200ms and stably works with a 1-point calibration showing a peak-to-peak error of ±2.35ºC, a resolution of 0.59ºC in a range of -10-to-100ºC. The second temperature sensor uses a scaled reference voltage obtained by switched capacitor circuits and an on-chip leakage-based oscillator for internal clock generation. The SAR ADC operates with a scaled supply voltage by 1/2 generated by the switched capacitor. The sensor consumes 487pW with a conversion time of 128.6ms at 20ºC. Peak-to-peak error is -3.43/2.77ºC and ±1.63ºC after 1-point and 2-point calibration, respectively. In a temperature range of -30 to 100ºC, the sensor shows resolution of 0.37ºC that is about 60% improved, compared with the first sensor. The designed sensors are fabricated in 180nm CMOS process

그래핀 기반 고성능 소자 제조를 위한 결함이 최소화된 화학기상증착 그래핀에 관한 연구

DoctorGraphene is a promising candidate for electronic devices, due to its exceptional electronic, mechanical and optical properties. Many efforts have been introduced to obtain large-area graphene with high quality for industrial applications. Graphene synthesized using chemical vapor deposition (CVD) is a strong candidate to meet this need. However, line defects, such as grain boundaries and wrinkles, are formed during CVD owing to uncontrollable nucleation and difference between graphene and catalytic substrate. Furthermore, in wide-area applications, the micro-structured and nano-structured graphene must be obtained by an intricate patterning process. Patterning methods composed of several steps such as lithography and etching can create point defects such as oxidized sites on graphene, and degrade its poor quality. This thesis presents a systematic investigation of various line defects (grain boundaries and wrinkles) on graphene and the development of bottom-up method to synthesize patterned graphene with minimal defects for high-quality graphene-based devices. In chapter 2, I develop an easy method to unveil the surface information of CVD-grown graphene by thermal evaporation of gold (Au) adatoms. Development of high-quality graphene-based electronics requires understanding of how line defects such as grain boundaries and wrinkles affect the electronic and mechanical properties of CVD-grown graphene. However, simultaneous visualization of both grain boundaries and wrinkles with detailed structural information has not been reported. Because defects have higher binding energy than that of intact graphene, thermal evaporation of Au adatoms induced selectively deposited gold particles near defect sites. Single lines and gold nanoparticles (Au NPs) formed along GBs, and double lines Au NPs formed along wrinkles. Furthermore, stitched grain boundaries can be distinguished from overlapped grain boundary, and standing wrinkles can be distinguished from folded wrinkles. The width of a standing collapsed wrinkle can be determined. Theoretical calculations revealed that morphology of defects on CVD-grown graphene is caused by distinct binding energies of defects, which affect diffusion of Au NPs. This systematic approach could be further extended to correlate line defects with their effects on electronic and mechanical properties of graphene. In chapter 3, I propose bottom-up method to synthesize patterned graphene with minimal defects from chemically-patterned polymer film as a solid carbon source. Precise graphene patterning is essential for graphene-based electronics. However, a top-down patterning process requires several steps such as lithography and etching, which inevitably cause point defects in the graphene lattice. To avoid these defects during patterning process, a bottom-up method to synthesize patterned graphene was used. The use of polymer as solid carbon source for graphene growth enables direct conversion of the polymer pattern to a graphene pattern. However, physically-patterned polymer film converts indirectly to graphene be deposition of hydrocarbon vapors that form when the polymer decomposes, and results in fully-grown graphene. Therefore, I used selectively-crosslinked polystyrene film as chemically patterned film and obtained bottom-up grown graphene/amorphous carbon (a-C) heterostructure pattern by using CVD. Graphene was successfully grown from neat polystyrene regions, whereas amorphous carbon (a-C) formed on patterned crosslinked polystyrene regions. Because the electrical conductivity of graphene is at least two orders of magnitude higher than that of a-C, the charge transport in graphene/a-C heterostructure mainly occurs through the graphene region. Measurement of the quantum Hall effect in graphene/a-C lateral heterostructures clearly confirms the reliable quality of graphene and the presence of a well-defined graphene/a-C interface. The direct synthesis of patterned graphene from polymer pattern could be further exploited to prepare versatile heterostructures

HLA-I 접합성에 따른 종양 가속화 평가 및 투명 세포 신장 세포 암에서 면역 특징의 발견

Clear cell renal cell carcinoma (ccRCC) is a common histological subtype of renal cancer with a 107% increase in incidence over about 20 years and has distinct immunogenic characteristics. CcRCC has been reported to have an immune characteristic contrary to the conventional notion, such as short survival despite abundance of tumor-infiltrating lymphocytes. In tumor immunity, the HLA-I molecule leads to tumor suppression, which enables CD8+ T cells to recognize tumors by presenting neoantigen, a peptide containing mutations in tumor cells, on the cell surface. We investigated tumor acceleration by HLA-I zygosity through tumor occurrence analysis in clear cell renal cell carcinoma as well as pan-cancer. To evaluate the effectiveness of immune surveillance by T cells, we selected early tumors close to the time point of immune evasion, excluding tumor samples containing pathogenic factors that influence tumor development. The zygosity of HLA-I was classified into homozygous group and heterozygous group based on the heterozygosity of all three classical HLA-I genes. The acceleration was assessed using an accelerated failure time (AFT) model by HLA zygosity. As a result, it was confirmed that heterozygous HLA-I delayed the tumor development in pan-cancer except ccRCC. In contrast, ccRCC was found to occur earlier in heterozygous HLA-I patients than homozygous HLA-I patients. To determine the cause of ccRCC acceleration in heterozygous HLA-I, we classified allele loss in major tumor suppressor genes, VHL and PBRM1. Tumor acceleration of heterozygous HLA-I was found to occur in tumors containing biallelic loss of VHL, according to the theory of the secondary hit hypothesis that the loss of both alleles results in a phenotypic change. The association of heterozygous HLA-I and VHL biallelic loss on tumor acceleration was validated in an independent ICGC clear cell renal cell carcinoma cohort. 투명 세포 신장 세포 암은 약 20년 동안 발병률이 107% 증가하는 신장암 의 하위유형 중 가장 흔한 암이며 뚜렷한 면역원성 특징을 갖는다. 특히 투명 세포 신장 세포 암은 종양 침윤 T 림프구가 많이 존재할 때 짧은 생존을 보이는 등 기존의 개념과는 반대되는 면역 특징이 보고되어져 왔 다. 종양 발생과정 중 면역반응을 설명하는 면역편집 이론은 최근 활발 히 연구되고 있으며, 면역편집 동안 CD8+ T 세포는 종양세포를 인지하 고 종양세포 특이적 사멸을 유발하는 반응을 한다. CD8+ T 세포가 종양 세포를 인식하는 반응에는 HLA-I 분자가 중요한 작용을 하게 되는데, HLA-I는 종양 특이적 항원인 신항원(neoantigen)을 세포표면으로 표지 하여 CD8+ T 세포가 non-self 항원인 neoantigen을 인지하여 반응을 유 발할 수 있게 한다. 본 연구는 HLA-I 접합성에 의한 종양 발병가속도를 조사하기 위해 TCGA의 대규모의 암 데이터를 이용하여 투명 세포 신장 세포 암 뿐만 아니라 범암(pan-cancer) 단위의 분석을 진행하였다. 병원 성 요인을 포함한 종양을 제외하여 T 세포에 의한 면역감시효과를 주요 하게 평가하였으며 면역회피가 일어난 시점에서 가장 가까운 초기 단계 의 종양을 선정하였다. HLA-I의 접합성은 HLA-I 유전자(HLA-A, B, C) 접합성에 따라 동형 접합, 이형 접합 HLA-I으로 분류되었고 HLA-I 접 합성의 종양 가속도를 측정하기 위해 accelerated failure time 모델이 사용되었다. 그 결과 투명 세포 신장 세포 암을 제외한 pan-cancer에서 이형 접합 HLA-I은 종양 발병이 늦춰지는 것과 연관성이 있었다. 대조 적으로 투명 세포 신장 세포 암에서는 이형 접합 HLA-I 환자에서 동형 접합 HLA-I 환자보다 일찍 종양이 발병하는 것이 밝혀졌다. 이형 접합 HLA-I에서 종양 가속화가 일어나는 원인을 규명하기 위해 투명 세포 신 장 세포 암에서 가장 빈번하게 돌연변이가 발생하는 종양 억제 유전자 VHL과 PBRM1를 선별하였다. VHL 유전자는 두 대립 유전자가 모두 손실 되면 표현형 변화가 생긴다는 two-hit hypothesis를 따르는 것이 보고 되어 왔으며, 이형 접합 HLA-I은 VHL 이중 대립 유전자 손실을 포함하 는 경우에서 유의한 종양 가속화를 나타냈다. 종양 가속화에 대한 이형 접합 HLA-I와 VHL 이중 대립 유전자 손실의 연관성은 독립적인 ICGC 투명 세포 신장 세포 암 집단에서 검증되었다.open석