High Thermoelectric Performance and Defect Energetics of Multipocketed Full Heusler Compounds

We report a first-principles density-functional study of electron-phonon interactions in and thermoelectric transport properties of the full Heusler compounds Sr2BiAu and Sr2SbAu. Our results show that ultrahigh intrinsic bulk thermoelectric performance across a wide range of temperatures is physically possible and point to the presence of multiply degenerate and highly dispersive carrier pockets as the key factor for achieving this. Sr2BiAu, which features ten energy-aligned low-effective-mass pockets (six along Γ-X and four at L), is predicted to deliver n-type zT=0.4-4.9 at T=100-700 K. Comparison with the previously investigated compound Ba2BiAu shows that the additional L pockets in Sr2BiAu significantly increase its low-temperature power factor to a maximum value of 12 mW m-1 K-2 near T=300 K. However, at high temperatures the power factor of Sr2BiAu drops below that of Ba2BiAu because the L states are heavier and subject to strong scattering by phonon deformation, as opposed to the lighter Γ-X states, which are limited by polar-optical scattering. Sr2SbAu is predicted to deliver a lower n-type zT=3.4 at T=750 K due to appreciable misalignment between the L and Γ-X carrier pockets, generally heavier scattering, and a slightly higher lattice thermal conductivity. Soft acoustic modes, which are responsible for the low lattice thermal conductivity, also increase the vibrational entropy and high-temperature stability of these Heusler compounds, suggesting that their experimental synthesis may be feasible. The dominant intrinsic defects are found to be Au vacancies, which drive the Fermi level towards the conduction band and work in favor of n-doping

Radiance and Doppler shift distributions across the network of the quiet Sun

The radiance and Doppler-shift distributions across the solar network provide observational constraints of two-dimensional modeling of transition-region emission and flows in coronal funnels. Two different methods, dispersion plots and average-profile studies, were applied to investigate these distributions. In the dispersion plots, we divided the entire scanned region into a bright and a dark part according to an image of Fe xii; we plotted intensities and Doppler shifts in each bin as determined according to a filtered intensity of Si ii. We also studied the difference in height variations of the magnetic field as extrapolated from the MDI magnetogram, in and outside network. For the average-profile study, we selected 74 individual cases and derived the average profiles of intensities and Doppler shifts across the network. The dispersion plots reveal that the intensities of Si ii and C iv increase from network boundary to network center in both parts. However, the intensity of Ne viii shows different trends, namely increasing in the bright part and decreasing in the dark part. In both parts, the Doppler shift of C iv increases steadily from internetwork to network center. The average-profile study reveals that the intensities of the three lines all decline from the network center to internetwork region. The binned intensities of Si ii and Ne viii have a good correlation. We also find that the large blue shift of Ne viii does not coincide with large red shift of C iv. Our results suggest that the network structure is still prominent at the layer where Ne viii is formed in the quiet Sun, and that the magnetic structures expand more strongly in the dark part than in the bright part of this quiet Sun region.Comment: 10 pages,9 figure

Dynamic responses of an elastic beam moving over a simple beam using modal superposition method

The dynamic responses of an elastic beam moving over a simple beam are investigated. The elastic beam is modeled as an Euler beam with both ends free, and connected to the simple beam by two spring units. With modal superposition method, the dynamic responses of these two beams are studied. The vibrations of the simple beam are almost the same due to the moving elastic beam and rigid beam, even the latter beam ignores the flexural vibration of the elastic beam. However, the acceleration of the moving elastic beam is much larger than that of the moving rigid beam, which can be attributed to the flexible vibration of the elastic beam. With various flexural stiffness of the elastic beam, the max accelerations of the elastic beam at midpoint are computed along with different moving velocities. It is observed that, with an increase of flexural stiffness of the elastic beam, the max acceleration of the elastic beam decreases evidently

Analytic Spectra of CMB Anisotropies and Polarization Generated by Relic Gravitational Waves with Modification due to Neutrino Free-Streaming

We present an analytical calculation of the spectra of CMB anisotropies and polarizations generated by relic gravitational waves (RGWs). As a substantial extension to the previous studies, three new ingredients are included in this work. Firstly, the analytic $C_l^{TT}$ and $C_l^{TE}$ are given; especially the latter can be useful to extract signal of RGWs from the observed data in the zero multipole method. Secondly, a fitting formula of the decaying factor on small scales is given, coming from the visibility function around the photon decoupling. Thirdly, the impacts by the neutrino free-streaming (NFS) is examined, a process that occurred in the early universe and leaves observable imprints on CMB via RGWs. It is found that the analytic $C_l^{TT}$ and $C_l^{TE}$ have profiles agreeing with the numeric ones, except that $C^{TT}_l$ in a range $l \le 10$ and the $1^{st}$ trough of $C_l^{TE}$ around $l \sim 75$ have some deviations. With the new damping factor, the analytic $C^{EE}_l$ and $C^{BB}_l$ match with the numeric ones with the maximum errors only $\sim 3$ up to the first three peaks for $l\le 600$, improving the previous studies substantially. The correspondence of the positions of peaks of $C^{XX}_l$ and those of RGWs are also demonstrated explicitly. We also find that NFS reduces the amplitudes of $C^{XX}_l$ by $(20$ for $l\simeq(100\sim 600)$ and shifts slightly their peaks to smaller angles. Detailed analyses show that the zero multipoles $l_0$, where $C_l^{TE}$ crosses 0, are shifted to larger values by NFS. This shifting effect is as important as those causedby different inflation models and different baryon fractions.Comment: 17 pages, 7 figures. accepted by PR

Tests of a Novel Design of Resistive Plate Chambers

A novel design of Resistive Plate Chambers (RPCs), using only a single resistive plate, is being proposed. Based on this design, two large size prototype chambers were constructed and were tested with cosmic rays and in particle beams. The tests confirmed the viability of this new approach. In addition to showing an improved single-particle response compared to the traditional 2-plate design, the novel chambers also prove to be suitable for calorimetric applications

Adversarial Sparse-View CBCT Artifact Reduction

We present an effective post-processing method to reduce the artifacts from sparsely reconstructed cone-beam CT (CBCT) images. The proposed method is based on the state-of-the-art, image-to-image generative models with a perceptual loss as regulation. Unlike the traditional CT artifact-reduction approaches, our method is trained in an adversarial fashion that yields more perceptually realistic outputs while preserving the anatomical structures. To address the streak artifacts that are inherently local and appear across various scales, we further propose a novel discriminator architecture based on feature pyramid networks and a differentially modulated focus map to induce the adversarial training. Our experimental results show that the proposed method can greatly correct the cone-beam artifacts from clinical CBCT images reconstructed using 1/3 projections, and outperforms strong baseline methods both quantitatively and qualitatively