Cation substitutional doping is an effective approach to modifying the electronic and thermal transports in Bi₂Te₃-based thermoelectric alloys. Here we present a comprehensive analysis of the ...electrical and thermal conductivities of polycrystalline Pb-doped p-type bulk Bi
Sb
Te₃. Pb doping significantly increased the electrical conductivity up to ~2700 S/cm at
= 0.02 in Bi
Pb
Sb
Te₃ due to the increase in hole carrier concentration. Even though the total thermal conductivity increased as Pb was added, due to the increased hole carrier concentration, the thermal conductivity was reduced by 14-22% if the contribution of the increased hole carrier concentration was excluded. To further understand the origin of reduction in the thermal conductivity, we first estimated the contribution of bipolar conduction to thermal conductivity from a two-parabolic band model, which is an extension of the single parabolic band model. Thereafter, the contribution of additional point defect scattering caused by Pb substitution (Pb in the cation site) was analyzed using the Debye-Callaway model. We found that Pb doping significantly suppressed both the bipolar thermal conduction and lattice thermal conductivity simultaneously, while the bipolar contribution to the total thermal conductivity reduction increased at high temperatures. At Pb doping of
= 0.02, the bipolar thermal conductivity decreased by ~30% from 0.47 W/mK to 0.33 W/mK at 480 K, which accounts for 70% of the total reduction.
Bi2Te3‐based materials have drawn much attention from the thermoelectric community due to their excellent thermoelectric performance near room temperature. However, the stability of existing n‐type ...Bi2(Te,Se)3 materials is still low due to the evaporation energy of Se (37.70 kJ mol−1) being much lower than that of Te (52.55 kJ mol−1). The evaporated Se from the material causes problems in interconnects of the module while degrading the efficiency. Here, we have developed a new approach for the high‐performance and stable n‐type Se‐free Bi2Te3‐based materials by maximizing the electronic transport while suppressing the phonon transport, at the same time. Spontaneously generated FeTe2 nanoinclusions within the matrix during the melt‐spinning and subsequent spark plasma sintering is the key to simultaneous engineering of the power factor and lattice thermal conductivity. The nanoinclusions change the fermi level of the matrix while intensifying the phonon scattering via nanoparticles. With a fine‐tuning of the fermi level with Cu doping in the n‐type Bi2Te3–0.02FeTe2, a high power factor of ~41 × 10−4 Wm−1 K−2 with an average zT of 1.01 at the temperature range 300–470 K are achieved, which are comparable to those obtained in n‐type Bi2(Te,Se)3 materials. The proposed approach enables the fabrication of high‐performance n‐type Bi2Te3‐based materials without having to include volatile Se element, which guarantees the stability of the material. Consequently, widespread application of thermoelectric devices utilizing the n‐type Bi2Te3‐based materials will become possible.
A novel approach for realizing high thermoelectric performance in Se‐free Bi2Te3‐based n‐type materials is proposed. FeTe2 nanoinclusions are spontaneously generated in Bi2Te3 alloys by controlling the cooling rate, which enhances electrical transport and phonon scattering effectively. Furthermore, additional Cu doping results in a high zT value of 1.08, which is an increase of over 60% compared with pure Bi2Te3.
Two-dimensional (2D) metal oxide nanosheets have been synthesized through ion exchange reactions. However, they require a long time and lead to low production yields due to the molecular size of the ...intercalant and reaction activation energies. To reduce the processing time and accelerate the production yield, we introduce an ultrasonically supported ion exchange reaction process. We applied ultrasound energy on the solution of RuO2 nanosheets and the intercalant after 3 days of stirring the ion exchange reaction. After 15 min, the yield of RuO2 nanosheets increased by over 50%. In addition, we observed that the lateral size of the RuO2 nanosheets decreased with the applied ultrasonic time. Density functional theory calculations demonstrated that the activation energy of exfoliation is significantly reduced by splitting the RuO2 layers into a small lateral size. This result shows that ultrasound provides energy for 15 min of exfoliation of the RuO2 nanosheets, after which the energy is used to break the RuO2 nanosheets. The experimental and theoretical results suggest that an ultrasonic-supported ion exchange process offers a facile and efficient approach for fabricating 2D metal oxide nanosheets.
In recent years, Mg and its alloys have attracted a great deal of attention due to their low density, relatively excellent castability, and straightforward recyclability. Mg alloys have been widely ...applied to various industrial fields, and are representatively used in automotive and electronic parts. According to previous researches, the electrical conductivity of Mg alloys greatly decreases with increasing Al content. However, with the addition of Zn and/or Cu, the electrical conductivity of Mg alloys is maintained or slightly increased, and improved mechanical properties are obtained as well. On this basis, Mg-Zn-Cu alloys have been investigated in the present study with a focus on the effect of adding Zn and Cu on the electrical conductivity. The Zn and Cu contents ranged from 4 to 6wt.% and 0 to 1.5wt.%, respectively. Ternary Mg-Zn-Cu alloys have been prepared by gravity casting in a steel mold. In the as-casting condition, the electrical conductivity of Mg-Zn-Cu alloys showed a linear increasing trend with decreasing Zn and increasing Cu contents. Furthermore, impact values of Zn = -1.5 and Cu = 2.5 were determined for these alloys by electrical conductivity tests.
A high-performance gas sensor operating at room temperature is always favourable since it simplifies the device fabrication and lowers the operating power by eliminating a heater. Herein, we ...fabricated the ammonia (NH
) gas sensor by using Au nanoparticle-decorated TiO
nanosheets, which were synthesized via two distinct processes: (1) preparation of monolayer TiO
nanosheets through flux growth and a subsequent chemical exfoliation and (2) decoration of Au nanoparticles on the TiO
nanosheets via hydrothermal method. Based on the morphological, compositional, crystallographic, and surface characteristics of this low-dimensional nano-heterostructured material, its temperature- and concentration-dependent NH
gas-sensing properties were investigated. A high response of ~ 2.8 was obtained at room temperature under 20 ppm NH
gas concentration by decorating Au nanoparticles onto the surface of TiO
nanosheets, which generated oxygen defects and induced spillover effect as well.
Abstract only
e14736
Background: To evaluate long-term survival in patients with unresectable hepatocellular carcinoma (HCC) in large national population-based database and to assess the impact of ...subspecialized care on similarly matched patients at a tertiary cancer center. Methods: Using the Surveillance, Epidemiology and End Results (SEER) registry, patients diagnosed between 2004 and 2008 with advanced unresectable HCC not amendable to radiation therapy or cancer-directed surgery were extracted. Additionally, similar matched patients receiving drug eluting bead transarterial chemoembolizaton (DEB TACE) for unresectable HCC were included in the study. Demographic, clinical, and procedural data were collected. Patients were stratified based on Contract Health Service Delivery Areas (CHSDA) and the rural- urban continuum. The Kaplan Meier method was used for survival analysis, and survival curves were compared using the log rank test in SPSS. Results: 14,369 patients were studied and demographics were as follows: mean age at time of diagnosis was 63.97 years (SD 12.5); 76.1% were male; 66.7% were Caucasian; 13.3% were African-American; and 19.4% were Asian or American Indian. The overall median observed survival from diagnosis of the 136 patients receiving DEB TACE was significantly higher when compared to the 404 Atlanta patients and the 12,012 SEER patients (median OS = 22 vs 4 vs 4 months respectively, p< 0.05). When compared to CHSDA, the median overall survival for patients receiving DEB TACE was 5 times longer than all other geographical areas (22 months vs 3, 4, 3, 4, and 4 in Alaska, East, Northern Plains, Pacific Coast, and the Southwest, respectively, p<0.05). Metropolitan, urban, and rural areas demonstrated similar survival outcomes and patients receiving DEB TACE had superior survival (22 vs 3-4 months, p<0.05). Conclusions: This study suggests that DEB TACE is viable treatment option that confers significantly beneficial survival results when compared to similar patients nationwide diagnosed with advanced unresectable HCC in the same 5-year time frame regardless of population demographics and health service delivery area.
In this paper, a new piezoelectric transducer for high performance ultrasonic flaw detector used in non-destructive test (NDT) is implemented. Here, the goals for some major characteristics such as ...piezoelectric strain constant and electro-mechanical coupling factor are fixed in advanced. Then, the parameters obtained by finite element analysis (FEA) are exploited to design and implement the piezoelectric transducer. As a result of experiments using manufactured samples, it is proved that the new PZT ceramics satisfy the goals very well. It has much improved impedance characteristic at the resonant frequency and generation of ultrasonic signals. In addition, ultrasonic flaw detector with the new transducer provides increased flaw detecting gain than the conventional one. Thus, it is considered that the new flaw detector contributes significantly to improve reliability of the NDT. 본 논문에서는 비파괴검사용 고성능 결함탐상기를 위한 압전변환기를 구현하였다. 여기서는 압전변형상수와 전기기계 결합계수 등과 같은 주요 특성에 대한 설계 목표치를 먼저 정하고 유한요소해석을 이용하여 얻은 데이터를 설계 및 제작에 활용하였다. 시편을 이용한 실험 결과, 제작된 PZT 세라믹은 목표치들을 매우 잘 만족시키는 것으로 확인되었다. 이는 공진 주파수에서 매우 향상된 임피던스 특성과 초음파 발생 특성을 가지는 것으로 나타났다. 또한 새로운 압전변환기가 적용된 초음파 결함탐상기는 기존 탐상기보다 증가된 결함 검출이득을 제공한다. 따라서 새로운 결함탐상기는 초음파를 이용한 비파괴검사의 검사 신뢰성 향상에 크게 기여할 수 있을 것으로 사료된다.
For more efficient power management in processors, a high-frequency and multi-phase (MP) integrated voltage regulator (IVR) using multiple inductors would be an ideal solution to deliver optimized ...power with rapid dynamic voltage scaling (DVS) 1-5. Nevertheless, in practical use, MP-IVRs suffer from an inter-inductor current imbalance because of mismatches in integrated inductances, different parasitic resistances, and duty-control skews among all phases (top of Fig. 18.1.1). Such a current mismatch may cause larger output ripple and efficiency degradation, losing the benefits of multi-phase operation. Also, thermal hotspots can occur due to excessive current density and deteriorate reliability. Previous approaches 2, 4 use current sensors to calibrate the duty cycle of each phase, but the design complexity and power overhead tend to be greatly increased in the high-speed sensing circuitry for fast-switching converters. An additional consideration in MP-IVRs is the phase-shedding technique, which can improve the light-load efficiency by reducing the number of phases. In many prior works 1, 2, the number of phases was adjusted by 2N (e.g., 1-2-4) for simplicity of phase division. If the phase-shedding is more fine-grained, the overall efficiency can be more flattened over a wide range of loads. Moreover, because the frequency response and output ripple vary according to the number of phases, the MP-IVR should be adaptively optimized further for them. This paper presents a 400MHz 6-phase fully integrated buck converter (bottom of Fig. 18.1.1). Key contributions of this work include 1) inter-inductor true-average-current matching by the flying-capacitor-based peak-and-valley differential sensing (PVDS) technique with near-zero power overhead, 2) area-efficient dynamic re-allocation of on-chip capacitors used either in the PVDS or at the output for optimizing responsiveness and voltage ripple adaptively to the number of phases, and 3) DLL -based multi-phase clock generation (MPCG) for fine-grained phase-shedding functionality, improving efficiency over a wide load range.
PDF
