Abstract
A quantum thermal machine is an open quantum system coupled to hot and cold thermal baths. Thus, its dynamics can be well understood using the concepts and tools from non-Hermitian quantum ...systems. A hallmark of non-Hermiticity is the existence of exceptional points where the eigenvalues of a non-Hermitian Hamiltonian or a Liouvillian superoperator and their associated eigenvectors coalesce. Here, we report the experimental realization of a single-ion heat engine and demonstrate the effect of Liouvillian exceptional points on the dynamics and the performance of a quantum heat engine. Our experiments have revealed that operating the engine in the exact- and broken-phases, separated by a Liouvillian exceptional point, respectively during the isochoric heating and cooling strokes of an Otto cycle produces more work and output power and achieves higher efficiency than executing the Otto cycle completely in the exact phase where the system has an oscillatory dynamics and higher coherence. This result opens interesting possibilities for the control of quantum heat engines and will be of interest to other research areas that are concerned with the role of coherence and exceptional points in quantum processes and in work extraction by thermal machines.
Quantum heat engines are expected to outperform the classical counterparts due to quantum coherences involved. Here we experimentally execute a single-ion quantum heat engine and demonstrate, for the ...first time, the dynamics and the enhanced performance of the heat engine originating from the Liouvillian exceptional points (LEPs). In addition to the topological effects related to LEPs, we focus on thermodynamic effects, which can be understood by the Landau-Zener-Stückelberg process under decoherence. We witness a positive net work from the quantum heat engine if the heat engine cycle dynamically encircles a LEP. Further investigation reveals that a larger net work is done when the system is operated closer to the LEP. We attribute the enhanced performance of the quantum heat engine to the Landau-Zener-Stückelberg process, enabled by the eigenenergy landscape in the vicinity of the LEP, and the exceptional point-induced topological transition. Therefore, our results open new possibilities toward LEP-enabled control of quantum heat engines and of thermodynamic processes in open quantum systems.
The measurement of Hubble constant (H0) is clearly a very important task in astrophysics and cosmology. Based on the principle of minimization of the information loss, we propose a robust most ...frequent value (MFV) procedure to determine H0, regardless of the Gaussian or non-Gaussian distributions. The updated data set of H0 contains the 591 measurements including the extensive compilations of Huchra and other researchers. The calculated result of the MFV is H0 = 67.498 km s−1 Mpc−1, which is very close to the average value of recent Planck H0 value (67.81 0.92 km s−1 Mpc−1 and 66.93 0.62 km s−1 Mpc−1) and Dark Energy Survey Year 1 Results. Furthermore, we apply the bootstrap method to estimate the uncertainty of the MFV of H0 under different conditions, and find that the 95% confidence interval for the MFV of H0 measurements is 66.319, 68.690 associated with statistical bootstrap errors, while a systematically larger estimate is H 0 = 67.498 − 3.278 + 7.970 (systematic uncertainty). Especially, the non-Normality of error distribution is again verified via the empirical distribution function test including Shapiro-Wilk test and Anderson-Darling test. These results illustrate that the MFV algorithm has many advantages in the analysis of such statistical problems, no matter what the distributions of the original measurements are.
ABSTRACT
SN 2018hti is a Type I superluminous supernova (SLSN I) with an absolute g-band magnitude of −22.2 at maximum brightness, discovered by the Asteroid Terrestrial-impact Last Alert System in a ...metal-poor galaxy at a redshift of 0.0612. We present extensive photometric and spectroscopic observations of this supernova, covering the phases from ∼−35 d to more than +340 d from the r-band maximum. Combining our BVgri-band photometry with Swift UVOT optical/ultraviolet photometry, we calculated the peak luminosity as ∼3.5 × 1044 erg s−1. Modelling the observed light curve reveals that the luminosity evolution of SN 2018hti can be produced by an ejecta mass of 5.8 M⊙ and a magnetar with a magnetic field of B = 1.8 × 1013 G having an initial spin period of P0 = 1.8 ms. Based on such a magnetar-powered scenario and a larger sample, a correlation between the spin of the magnetar and the kinetic energy of the ejecta can be inferred for most SLSNe I, suggesting a self-consistent scenario. Like for other SLSNe I, the host galaxy of SN 2018hti is found to be relatively faint (Mg = −17.75 mag) and of low metallicity (Z = 0.3 Z⊙), with a star formation rate of 0.3 M⊙ yr−1. According to simulation results of single-star evolution, SN 2018hti could originate from a massive, metal-poor star with a zero-age main sequence (ZAMS) mass of 25–40 M⊙, or from a less massive rotating star with MZAMS ≈ 16–25 M⊙. For the case of a binary system, its progenitor could also be a star with $M_\mathrm{ZAMS} \gtrsim 25\, \mathrm{ M}_\odot$.
In this work, the electronic properties of phosphorene nanoribbons with different width and edge configurations are studied by using density functional theory. It is found that the armchair ...phosphorene nanoribbons are semiconducting while the zigzag nanoribbons are metallic. The band gaps of armchair nanoribbons decrease monotonically with increasing ribbon width. By passivating the edge phosphorus atoms with hydrogen, the zigzag series also become semiconducting, while the armchair series exhibit a larger band gap than their pristine counterpart. The electronic transport properties of these phosphorene nanoribbons are then investigated using Boltzmann theory and relaxation time approximation. We find that all the semiconducting nanoribbons exhibit very large values of Seebeck coefficient and can be further enhanced by hydrogen passivation at the edge. Taking pristine armchair nanoribbons and hydrogen-passivated zigzag naoribbons with width N = 7, 8, 9 as examples, we calculate the lattice thermal conductivity with the help of phonon Boltzmann transport equation and evaluate the width-dependent thermoelectric performance. Due to significantly enhanced Seebeck coefficient and decreased thermal conductivity, we find that at least one type of phosphorene nanoribbons can be optimized to exhibit very high figure of merit (ZT values) at room temperature, which suggests their appealing thermoelectric applications.
Summary
Hepatitis B virus surface antigen (HBsAg) plays an important role in maintaining the tolerance and may interfere with host innate and adaptive immune responses; therefore, novel therapeutic ...strategies to reduce HBsAg loads in patients infected with hepatitis B virus (HBV) are emerging as an attractive but challenging issue. Metformin could regulate hepatic metabolism while the latter interacts with HBV infection. We hypothesized that metformin could affect HBsAg expression and HBV replication and may work synergistically when combined with current antivirals. In our study, a notably inhibitory effect on HBsAg production, as well as a moderate inhibition in HBV replication and HBeAg expression was observed following metformin treatment. The 50% effective concentration (EC50) for extracellular HBsAg and intracellular HBsAg in HBV‐producing HepG2.2.15 cells was 2.85 mm and 2.75 mm, respectively, with a similarly selective index of about 18. When administered in combination, metformin enhanced the inhibitory effects of interferon‐α2b on HBsAg expression and HBV replication and provided a complimentary role in HBsAg expression for lamivudine (LMV). This novel action of metformin derives partially from its inhibition on multiple HBV cis‐acting elements. By the virtues of preferably hepatocyte distribution and safety profile, collectively, our results suggest that metformin would be potentially clinically helpful as an HBsAg production inhibitor.
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