Abstract
Gravitational waves emitted from stellar binary black hole (sBBH) mergers can be gravitationally lensed by intervening galaxies and detected by future ground-based detectors. A great amount ...of effort has been put into the estimation of the detection rate of lensed sBBH originating from the evolution of massive binary stars (EMBS channel). However, sBBHs produced by the dynamical interaction in dense clusters (dynamical channel) may also be dominant in our universe and their intrinsic distribution of physical properties can be significantly different from those produced by massive stars, especially mass and redshift distribution. In this paper, we investigate the event rate of lensed sBBHs produced via the dynamical channel by Monte Carlo simulations and the number is
16
−
12
+
4.7
yr
−1
for the Einstein telescope and
24
−
17
+
6.8
yr
−1
for Cosmic Explorer, of which the median is about ∼2 times the rate of sBBHs originating from the EMBS channel (calibrated by the local merger rate density estimated for the dynamical and the EMBS channel, i.e.,
∼
14
−
10
+
4.0
and
19
−
3.0
+
42
Gpc
−
3
yr
−
1
, respectively). Therefore, one may constrain the fraction of both the EMBS and dynamical channels through the comparison of the predicted and observed number of lensed sBBH events statistically.
For several decades, thermoelectric advancements have largely relied on the reduction of lattice thermal conductivity (κL). According to the Boltzmann transport theory of phonons, κL mainly depends ...on the specific heat, the velocity, and the scattering of phonons. Intensifying the scattering rate of phonons is the focus for reducing the lattice thermal conductivity. Effective scattering sources include 0D point defects, 1D dislocations, and 2D interfaces, each of which has a particular range of frequencies where phonon scattering is most effective. Because acoustic phonons are generally the main contributors to κL due to their much higher velocities compared to optical phonons, many low‐κL thermoelectrics rely on crystal structure complexity leading to a small fraction of acoustic phonons and/or weak chemical bonds enabling an overall low phonon propagation velocity. While these thermal strategies are successful for advancing thermoelectrics, the principles used can be integrated with approaches such as band engineering to improve the electronic properties, which can promote this energy technology from niche applications into the mainstream.
Phonon transport is reviewed, considering its guiding principles, and including a summary of newly proven strategies and further considerations for κL‐minimization. Most of the strategies presented can effectively reduce the lattice thermal conductivity, which leads to a great increase in thermoelectric performance in many materials.
High-efficiency thermoelectric materials require a high conductivity. It is known that a large number of degenerate band valleys offers many conducting channels for improving the conductivity without ...detrimental effects on the other properties explicitly, and therefore, increases thermoelectric performance. In addition to the strategy of converging different bands, many semiconductors provide an inherent band nestification, equally enabling a large number of effective band valley degeneracy. Here we show as an example that a simple elemental semiconductor, tellurium, exhibits a high thermoelectric figure of merit of unity, not only demonstrating the concept but also filling up the high performance gap from 300 to 700 K for elemental thermoelectrics. The concept used here should be applicable in general for thermoelectrics with similar band features.
Compared to commercially available p‐type PbTe thermoelectrics, SnTe has a much bigger band offset between its two valence bands and a much higher lattice thermal conductivity, both of which limit ...its peak thermoelectric figure of merit, zT of only 0.4. Converging its valence bands or introducing resonant states is found to enhance the electronic properties, while nanostructuring or more recently introducing interstitial defects is found to reduce the lattice thermal conductivity. Even with an integration of some of the strategies above, existing efforts do not enable a peak zT exceeding 1.4 and usually involve Cd or Hg. In this work, a combination of band convergence and interstitial defects, each of which enables a ≈150% increase in the peak zT, successfully accumulates the zT enhancements to be ≈300% (zT up to 1.6) without involving any toxic elements. This opens new possibilities for further improvements and promotes SnTe as an environment‐friendly solution for conventional p‐PbTe thermoelectrics.
A combination of band convergence by alloying with MnTe and interstitial defect scattering by alloying with Cu2Te, each of which enables an ≈150% increase in the peak thermoelectric figure of merit, zT of SnTe, successfully accumulates the zT enhancements to be ≈300% without involving any toxic elements. This promotes SnTe as an eco‐friendly solution for p‐PbTe thermoelectrics.
To minimize the lattice thermal conductivity in thermoelectrics, strategies typically focus on the scattering of low-frequency phonons by interfaces and high-frequency phonons by point defects. In ...addition, scattering of mid-frequency phonons by dense dislocations, localized at the grain boundaries, has been shown to reduce the lattice thermal conductivity and improve the thermoelectric performance. Here we propose a vacancy engineering strategy to create dense dislocations in the grains. In Pb
Sb
Se solid solutions, cation vacancies are intentionally introduced, where after thermal annealing the vacancies can annihilate through a number of mechanisms creating the desired dislocations homogeneously distributed within the grains. This leads to a lattice thermal conductivity as low as 0.4 Wm
K
and a high thermoelectric figure of merit, which can be explained by a dislocation scattering model. The vacancy engineering strategy used here should be equally applicable for solid solution thermoelectrics and provides a strategy for improving zT.
Phonon scattering by nanostructures and point defects has become the primary strategy for minimizing the lattice thermal conductivity (κL) in thermoelectric materials. However, these scatterers are ...only effective at the extremes of the phonon spectrum. Recently, it has been demonstrated that dislocations are effective at scattering the remaining mid‐frequency phonons as well. In this work, by varying the concentration of Na in Pb0.97Eu0.03Te, it has been determined that the dominant microstructural features are point defects, lattice dislocations, and nanostructure interfaces. This study reveals that dense lattice dislocations (≈4 × 1012 cm−2) are particularly effective at reducing κL. When the dislocation concentration is maximized, one of the lowest κL values reported for PbTe is achieved. Furthermore, due to the band convergence of the alloyed 3% mol. EuTe the electronic performance is enhanced, and a high thermoelectric figure of merit, zT, of ≈2.2 is achieved. This work not only demonstrates the effectiveness of dense lattice dislocations as a means of lowering κL, but also the importance of engineering both thermal and electronic transport simultaneously when designing high‐performance thermoelectrics.
Eu‐doping effectively converges the valence bands of PbTe, while Na‐doping enables dense lattice dislocations, leading to an extremely low lattice thermal conductivity (κL) of <0.4 W m−1 K−1. This contributes to a high zT of ≈2.2, opening new possibilities for advancing thermoelectrics through dislocation and band‐engineering approaches.
Advancing thermoelectric n‐type Mg3Sb2 alloys requires both high carrier concentration offered by effective doping and high carrier mobility enabled by large grains. Existing research usually ...involves chalcogen doping on the anion sites, and the resultant carrier concentration reaches ≈3 × 1019 cm−3 or below. This is much lower than the optimum theoretically predicted, which suggets that further improvements will be possible once a highly efficient dopant is found. Yttrium, a trivalent dopant, is shown to enable carrier concentrations up to and above ≈1 × 1020 cm−3 when it is doped on the cation site. Such carrier concentration allows for in‐depth understand of the electronic transport properties over a broad range of carrier concentrations, based on a single parabolic band approximation. As well as reasonably high carrier mobility in coarse‐grain materials sintered by hot deforming and fusing of large pieces of ingots synthesized by melting, higher thermoelectric performance than earlier experimentally reported for n‐type Mg3Sb2 is found. In particular, the thermoelectric figure of merit, zT, is even higher than that of any known n‐type thermoelectric, including Bi2Te3 alloys, within 300–500 K. This might pave the way for Mg3Sb2 alloys to become a realistic material for n‐type thermoelectrics for sustainable applications.
Yttrium is found to be an effective dopant for obtaining electron concentrations as high as ≈1020 cm−3 in Mg3SbBi. This leads to extraordinary thermoelectric performance and high thermal stability.
Coronavirus disease 2019 (COVID-19) causes severe community and nosocomial outbreaks. Comprehensive data for serial respiratory viral load and serum antibody responses from patients infected with ...severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are not yet available. Nasopharyngeal and throat swabs are usually obtained for serial viral load monitoring of respiratory infections but gathering these specimens can cause discomfort for patients and put health-care workers at risk. We aimed to ascertain the serial respiratory viral load of SARS-CoV-2 in posterior oropharyngeal (deep throat) saliva samples from patients with COVID-19, and serum antibody responses.
We did a cohort study at two hospitals in Hong Kong. We included patients with laboratory-confirmed COVID-19. We obtained samples of blood, urine, posterior oropharyngeal saliva, and rectal swabs. Serial viral load was ascertained by reverse transcriptase quantitative PCR (RT-qPCR). Antibody levels against the SARS-CoV-2 internal nucleoprotein (NP) and surface spike protein receptor binding domain (RBD) were measured using EIA. Whole-genome sequencing was done to identify possible mutations arising during infection.
Between Jan 22, 2020, and Feb 12, 2020, 30 patients were screened for inclusion, of whom 23 were included (median age 62 years range 37–75). The median viral load in posterior oropharyngeal saliva or other respiratory specimens at presentation was 5·2 log10 copies per mL (IQR 4·1–7·0). Salivary viral load was highest during the first week after symptom onset and subsequently declined with time (slope −0·15, 95% CI −0·19 to −0·11; R2=0·71). In one patient, viral RNA was detected 25 days after symptom onset. Older age was correlated with higher viral load (Spearman's ρ=0·48, 95% CI 0·074–0·75; p=0·020). For 16 patients with serum samples available 14 days or longer after symptom onset, rates of seropositivity were 94% for anti-NP IgG (n=15), 88% for anti-NP IgM (n=14), 100% for anti-RBD IgG (n=16), and 94% for anti-RBD IgM (n=15). Anti-SARS-CoV-2-NP or anti-SARS-CoV-2-RBD IgG levels correlated with virus neutralisation titre (R2>0·9). No genome mutations were detected on serial samples.
Posterior oropharyngeal saliva samples are a non-invasive specimen more acceptable to patients and health-care workers. Unlike severe acute respiratory syndrome, patients with COVID-19 had the highest viral load near presentation, which could account for the fast-spreading nature of this epidemic. This finding emphasises the importance of stringent infection control and early use of potent antiviral agents, alone or in combination, for high-risk individuals. Serological assay can complement RT-qPCR for diagnosis.
Richard and Carol Yu, May Tam Mak Mei Yin, The Shaw Foundation Hong Kong, Michael Tong, Marina Lee, Government Consultancy Service, and Sanming Project of Medicine.
In this work, a water splitting photoanode composed of a BiVO4 thin film surface modified by the deposition of a rhodium (Rh)‐doped SrTiO3 perovskite is fabricated, and the Rh‐doped SrTiO3 outer ...layer exhibits special photoelectrochemical (PEC) oxygen evolution co‐catalytic activity. Controlled intensity modulated photo‐current spectroscopy, electrochemical impedance spectroscopy, and other electrochemical results indicate that the Rh on the perovskite provide an oxidation active site during the PEC water oxidation process by reducing the reaction energy barrier for water oxidation. Theoretical calculations indicate that the water oxidation reaction is more likely to occur on the (110) crystal plane of Rh‐SrTiO3 because the oxygen evolution reaction overpotential on the (110) crystal plane is reduced significantly. Therefore, the obtained BiVO4/Rh5%‐SrTiO3 photoanode exhibits an optimized PEC performance. In particular, it facilitates the saturation of the photocurrent density. Thus, the presence of doped Rh in SrTiO3 can reduce the amount of noble metals required while achieving excellent and stable oxygen evolution properties.
The oxygen evolution reaction (OER) cocatalytic performance of Rh‐doped perovskite SrTiO3
is researched. Rh provides the main active sites for the OER and the overpotential over the Rh‐SrTiO3 (110) facet is significantly reduced. Rh‐doped SrTiO3 greatly reduces the amount of noble metals, but displays excellent oxygen evolution properties. It also takes into account the stability of perovskite materials.
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