The formula for maximum efficiency ( η âââ) of heat conversion into electricity by a thermoelectric device in terms of the dimensionless figure of merit ( ZT ) has been widely used to assess ...the desirability of thermoelectric materials for devices. Unfortunately, the η âââ values vary greatly depending on how the average ZT values are used, raising questions about the applicability of ZT in the case of a large temperature difference between the hot and cold sides due to the neglect of the temperature dependences of the material properties that affect ZT . To avoid the complex numerical simulation that gives accurate efficiency, we have defined an engineering dimensionless figure of merit ( ZT ) ââg and an engineering power factor ( PF ) ââg as functions of the temperature difference between the cold and hot sides to predict reliably and accurately the practical conversion efficiency and output power, respectively, overcoming the reporting of unrealistic efficiency using average ZT values.
Conventional theory predicts that ultrahigh lattice thermal conductivity can only occur in crystals composed of strongly bonded light elements, and that it is limited by anharmonic three-phonon ...processes. We report experimental evidence that departs from these long-held criteria. We measured a local room-temperature thermal conductivity exceeding 1000 watts per meter-kelvin and an average bulk value reaching 900 watts per meter-kelvin in bulk boron arsenide (BAs) crystals, where boron and arsenic are light and heavy elements, respectively. The high values are consistent with a proposal for phonon-band engineering and can only be explained by higher-order phonon processes. These findings yield insight into the physics of heat conduction in solids and show BAs to be the only known semiconductor with ultrahigh thermal conductivity.
Background & Aims The incidence of hepatocellular carcinoma (HCC) increases with age, but protective antibody responses decrease with time after infants are immunized against hepatitis B virus (HBV). ...We investigated whether immunization of infants against HBV prevents their developing HCC as adults. We also searched for strategies to maximize the cancer-preventive effects. Methods We collected data from 2 Taiwan HCC registry systems on 1509 patients (6–26 years old) diagnosed with HCC from 1983 through 2011. Data on history of HBV immunization and prenatal maternal levels of HBV antigens of all HCC patients born after July 1984 were retrieved from the HBV immunization data bank of the Taiwan Center for Disease Control. We collected data on birth cohort-specific populations (6–26 years old) of Taiwan using the National Household Registry System. Rates of HCC incidence per 105 person-years were derived by dividing the number of patients with HCC by the person-years of the general population. Relative risks (RR) for HCC were estimated by Poisson regression analysis in vaccinated vs unvaccinated birth cohorts. We stratified patients by age group to evaluate the association of birth cohorts and HCC risks. Results Of the 1509 patients with HCC, 1343 were born before, and 166 were born after, the HBV vaccination program began. HCC incidence per 105 person-years was 0.92 in the unvaccinated cohort and 0.23 in the vaccinated birth cohorts. The RRs for HCC in patients 6–9 years old, 10–14 years old, 15–19 years old, and 20–26 years old who were vaccinated vs unvaccinated were 0.26 (95% confidence interval CI, 0.17–0.40), 0.34 (95% CI, 0.25–0.48), 0.37 (95% CI, 0.25–0.51), and 0.42 (95% CI, 0.32–0.56), respectively. The RR for HCC in 6- to 26-year-olds was lower in the later vs the earlier cohorts (born in 1992–2005 vs 1986–1992; P < .001 and 1986–1992 vs 1984–1986; P < .002). Transmission of HBV from highly infectious mothers and incomplete immunization were associated with development of HCC. Conclusions Based on an analysis of 1509 patients with HCC in Taiwan, immunization of infants against HBV reduces their risk of developing HCC as children and young adults. Improving HBV vaccination strategies and overcoming risk factors could reduce the incidence of liver cancer.
Commercial hydrogen production by electrocatalytic water splitting will benefit from the realization of more efficient and less expensive catalysts compared with noble metal catalysts, especially for ...the oxygen evolution reaction, which requires a current density of 500 mA/cm² at an overpotential below 300 mV with long-term stability. Here we report a robust oxygen-evolving electrocatalyst consisting of ferrous metaphosphate on self-supported conductive nickel foam that is commercially available in large scale. We find that this catalyst, which may be associated with the in situ generated nickel–iron oxide/hydroxide and iron oxyhydroxide catalysts at the surface, yields current densities of 10 mA/cm² at an overpotential of 177 mV, 500 mA/cm² at only 265 mV, and 1,705 mA/cm² at 300 mV, with high durability in alkaline electrolyte of 1 M KOH even after 10,000 cycles, representing activity enhancement by a factor of 49 in boosting water oxidation at 300 mV relative to the state-of-the-art IrO₂ catalyst.
Achieving higher carrier mobility plays a pivotal role for obtaining potentially high thermoelectric performance. In principle, the carrier mobility is governed by the band structure as well as by ...the carrier scattering mechanism. Here, we demonstrate that by manipulating the carrier scattering mechanism in n-type Mg₃Sb₂-based materials, a substantial improvement in carrier mobility, and hence the power factor, can be achieved. In this work, Fe, Co, Hf, and Ta are doped on the Mg site of Mg3.2Sb1.5Bi0.49Te0.01, where the ionized impurity scattering crosses over to mixed ionized impurity and acoustic phonon scattering. A significant improvement in Hall mobility from ∼16 to ∼81 cm²·V−1·s−1 is obtained, thus leading to a notably enhanced power factor of ∼13 μW·cm−1·K−2 from ∼5 μW·cm−1·K−2. A simultaneous reduction in thermal conductivity is also achieved. Collectively, a figure of merit (ZT) of ∼1.7 is obtained at 773 K in Mg3.1Co0.1Sb1.5Bi0.49Te0.01. The concept of manipulating the carrier scattering mechanism to improve the mobility should also be applicable to other material systems.
Improvements in thermoelectric material performance over the past two decades have largely been based on decreasing the phonon thermal conductivity. Enhancing the power factor has been less ...successful in comparison. In this work, a peak power factor of ∼106 μW·cm−1·K−2 is achieved by increasing the hot pressing temperature up to 1,373 K in the p-type half-Heusler Nb0.95Ti0.05FeSb. The high power factor subsequently yields a record output power density of ∼22 W·cm−2 based on a single-leg device operating at between 293 K and 868 K. Such a high-output power density can be beneficial for large-scale power generation applications.
This work presents a fall detection system that is worn on the head, where the acceleration and posture are stable such that everyday movement can be identified without disturbing the wearer. Falling ...movements are recognized by comparing the acceleration and orientation of a wearer's head using prespecified thresholds. The proposed system consists of a triaxial accelerometer, gyroscope, and magnetometer; as such, a Madgwick's filter is adopted to improve the accuracy of the estimation of orientation. Moreover, with its integrated Wi-Fi module, the proposed system can notify an emergency contact in a timely manner to provide help for the falling person. Based on experimental results concerning falling movements and activities of daily living, the proposed system achieved a sensitivity of 96.67% in fall detection, with a specificity of 98.27%, and, therefore, is suitable for detecting falling movements in daily life.
Summary
Background
While direct‐acting antivirals have been approved for treating hepatitis C, the guidelines highlight the importance of considering potential drug‐drug interactions between DAAs and ...concomitant medications.
Aim
To assess comorbidity prevalence, concomitant medication use and potential drug‐drug interactions between DAAs and concomitant medications for hepatitis C patients in Taiwan.
Methods
This cross‐sectional study enrolled 822 patients from May to August 2016 in Taiwan. Patient demographics, comorbidities and concomitant medications were evaluated by physician surveys.
Results
A total of 709 (86.3%) patients had ≥1 comorbidity; the most prevalent comorbidity categories were diseases of the digestive system (40.1%), circulatory system (38.7%) and endocrine/nutritional/metabolic diseases (35.2%). Elderly patients had more comorbidities. A total of 622 (75.7%) patients received ≥1 concomitant medication; the average number of concomitant medications was 3.2. The most common concomitant medication classes were cardiovascular (34.4%), gastrointestinal (25.7%) and central nervous system drugs (22.7%). Among patients without cirrhosis or with compensated cirrhosis, contraindications were most prevalent with paritaprevir/ritonavir/ombitasvir plus dasabuvir, daclatasvir/asunaprevir and glecaprevir/pibrentasvir (13.3%, 6.0% and 5.4% respectively), and least prevalent with sofosbuvir, sofosbuvir/daclatasvir, sofosbuvir/ledipasvir and sofosbuvir/velpatasvir (0.8%, 1.3%, 1.4% and 2.1% respectively). Sofosbuvir‐based regimens had no contraindications in patients with decompensated cirrhosis.
Conclusion
Our population represented an elderly demographic, with a high prevalence of comorbidities and widespread use of concomitant medications. The potential drug‐drug interactions between these concomitant medications and DAA regimens differed, with the fewest potential interactions with sofosbuvir‐based regimens.
Thermoelectric power generation is one of the most promising techniques to use the huge amount of waste heat and solar energy. Traditionally, high thermoelectric figure-of-merit, ZT , has been the ...only parameter pursued for high conversion efficiency. Here, we emphasize that a high power factor ( PF ) is equivalently important for high power generation, in addition to high efficiency. A new n-type Mg ₂Sn-based material, Mg ₂Sn ₀.₇₅Ge ₀.₂₅, is a good example to meet the dual requirements in efficiency and output power. It was found that Mg ₂Sn ₀.₇₅Ge ₀.₂₅ has an average ZT of 0.9 and PF of 52 μW⋅cm ⁻¹⋅K ⁻² over the temperature range of 25–450 °C, a peak ZT of 1.4 at 450 °C, and peak PF of 55 μW⋅cm ⁻¹⋅K ⁻² at 350 °C. By using the energy balance of one-dimensional heat flow equation, leg efficiency and output power were calculated with T ₕ = 400 °C and T c = 50 °C to be of 10.5% and 6.6 W⋅cm ⁻² under a temperature gradient of 150 °C⋅mm ⁻¹, respectively.
Significance Thermoelectric materials have been extensively studied for applications in conversion of waste heat into electricity. The efficiency is related to the figure-of-merit, ZT = ( S ²σ / κ ) T , where S , σ , and κ are the Seebeck coefficient, electrical conductivity, and thermal conductivity, respectively. Pursuing higher ZT for higher efficiency has been the focus by mainly reducing the thermal conductivity. In this paper, we point out, for a given ZT , higher power factor ( S ²σ ) should be pursued for achieving more power because power is determined by ( T ₕ − T c) ²( S ²σ )/ L , where T ₕ, T c, and L are the hot and cold side temperatures, and leg length, respectively. We found a new material, Mg ₂Sn ₀.₇₅Ge ₀.₂₅, having both high ZT and high power factor.
Abstract
The efficiency of sunlight-driven reduction of carbon dioxide (CO
2
), a process mimicking the photosynthesis in nature that integrates the light harvester and electrolysis cell to convert ...CO
2
into valuable chemicals, is greatly limited by the sluggish kinetics of oxygen evolution in pH-neutral conditions. Current non-noble metal oxide catalysts developed to drive oxygen evolution in alkaline solution have poor performance in neutral solutions. Here we report a highly active and stable oxygen evolution catalyst in neutral pH, Brownmillerite Sr
2
GaCoO
5
, with the specific activity about one order of magnitude higher than that of widely used iridium oxide catalyst. Using Sr
2
GaCoO
5
to catalyze oxygen evolution, the integrated CO
2
reduction achieves the average solar-to-CO efficiency of 13.9% with no appreciable performance degradation in 19 h of operation. Our results not only set a record for the efficiency in sunlight-driven CO
2
reduction, but open new opportunities towards the realization of practical CO
2
reduction systems.
PDF
