72 research outputs found
Tetris-inspired detector with neural network for radiation mapping
In recent years, radiation mapping has attracted widespread research
attention and increased public concerns on environmental monitoring. In terms
of both materials and their configurations, radiation detectors have been
developed to locate the directions and positions of the radiation sources. In
this process, algorithm is essential in converting detector signals to
radiation source information. However, due to the complex mechanisms of
radiation-matter interaction and the current limitation of data collection,
high-performance, low-cost radiation mapping is still challenging. Here we
present a computational framework using Tetris-inspired detector pixels and
machine learning for radiation mapping. Using inter-pixel padding to increase
the contrast between pixels and neural network to analyze the detector
readings, a detector with as few as four pixels can achieve high-resolution
directional mapping. By further imposing Maximum a Posteriori (MAP) with a
moving detector, further radiation position localization is achieved.
Non-square, Tetris-shaped detector can further improve performance beyond the
conventional grid-shaped detector. Our framework offers a new avenue for high
quality radiation mapping with least number of detector pixels possible, and is
anticipated to be capable to deploy for real-world radiation detection with
moderate validation.Comment: 29 pages, 20 figures. Ryotaro Okabe and Shangjie Xue contributed
equally to this wor
Pressure induced superconductivity in WB2 and ReB2 through modifying the B layers
The recent discovery of superconductivity up to 32 K in the pressurized MoB2
reignites the interests in exploring high-Tc superconductors in
transition-metal diborides. Inspired by that work, we turn our attention to the
5d transition-metal diborides. Here we systematically investigate the responses
of both structural and physical properties of WB2 and ReB2 to external
pressure, which possess different types of boron layers. Similar to MoB2, the
pressure-induced superconductivity was also observed in WB2 above 60 GPa with a
maximum Tc of 15 K at 100 GPa, while no superconductivity was detected in ReB2
in this pressure range. Interestingly, the structures at ambient pressure for
both WB2 and ReB2 persist to high pressure without structural phase
transitions. Theoretical calculations suggest that the ratio of flat boron
layers in this class of transition-metal diborides may be crucial for the
appearance of high Tc. The combined theoretical and experimental results
highlight the effect of geometry of boron layers on superconductivity and shed
light on the exploration of novel high-Tc superconductors in borides.Comment: 17 pages,5 figure
Nearly-room-temperature ferromagnetism and tunable anomalous Hall effect in atomically thin Fe4CoGeTe2
Itinerant ferromagnetism at room temperature is a key ingredient for spin
transport and manipulation. Here, we report the realization of
nearly-room-temperature itinerant ferromagnetism in Co doped Fe5GeTe2 thin
flakes. The ferromagnetic transition temperature TC (323 K - 337 K) is almost
unchanged when thickness is down to 12 nm and is still about 284 K at 2 nm
(bilayer thickness). Theoretical calculations further indicate that the
ferromagnetism persists in monolayer Fe4CoGeTe2. In addition to the robust
ferromagnetism down to the ultrathin limit, Fe4CoGeTe2 exhibits an unusual
temperature- and thickness-dependent intrinsic anomalous Hall effect. We
propose that it could be ascribed to the dependence of band structure on
thickness that changes the Berry curvature near the Fermi energy level subtly.
The nearly-room-temperature ferromagnetism and tunable anomalous Hall effect in
atomically thin Fe4CoGeTe2 provide opportunities to understand the exotic
transport properties of two-dimensional van der Waals magnetic materials and
explore their potential applications in spintronics.Comment: 28 pages, 4 figures, 1 tabl
On-chip three-dimensional high-Q microcavities fabricated by femtosecond laser direct writing
We report on the fabrication of three-dimensional (3D) high-Q whispering
gallery microcavities on a fused silica chip by femtosecond laser
microfabriction, enabled by the 3D nature of femtosecond laser direct writing.
The processing mainly consists of formation of freestanding microdisks by
femtosecond laser direct writing and subsequent wet chemical etching. CO2 laser
annealing is followed to smooth the microcavity surface. Microcavities with
arbitrary tilting angle, lateral and vertical positioning are demonstrated, and
the quality (Q)-factor of a typical microcavity is measured to be up to
1.07x10^6, which is currently limited by the low spatial resolution of motion
stage used during the laser patterning and can be improved with motion stages
of higher resolutions.Comment: 17 pages, 3 figure
Eightfold Fermionic Excitation in a Charge Density Wave Compound
Unconventional quasiparticle excitations in condensed matter systems have
become one of the most important research frontiers. Beyond two- and fourfold
degenerate Weyl and Dirac fermions, three-, six- and eightfold symmetry
protected degeneracies have been predicted however remain challenging to
realize in solid state materials. Here, charge density wave compound TaTe4 is
proposed to hold eightfold fermionic excitation and Dirac point in energy
bands. High quality TaTe4 single crystals are prepared, where the charge
density wave is revealed by directly imaging the atomic structure and a
pseudogap of about 45 meV on the surface. Shubnikov de-Haas oscillations of
TaTe4 are consistent with band structure calculation. Scanning tunneling
microscopy reveals atomic step edge states on the surface of TaTe4. This work
uncovers that charge density wave is able to induce new topological phases and
sheds new light on the novel excitations in condensed matter materials.Comment: Accepted by PRB:
https://journals.aps.org/prb/accepted/7907cK4eW0b1ee0b93fd67c1b42942bbb08eafc3
Comparison of Macroeconomic Factors Explanatory Power Between Chinese and Swedish Stock Market
In order to seek the difference between Chinese and Swedish stock market, this thesis makes a comparison of explanatory power of macroeconomic factors between the stock markets in respective country. The vector autoregressive (VAR) models are implemented to analyze the relationship among the market returns and macroeconomic variables, i.e., GDP, CPI, exchange rate, unemployment rate and interbank offered rate in China and Sweden. The empirical result illustrated that Chinese stock market is more sensitive to the changes of macroeconomic variables than Swedish stock market. To make a clear interpretation for the estimation result, impulse responses functions and variance decompositions are applied to support the empirical test. Moreover, we analyzed the potential reasons that may cause the differences between Chinese and Swedish stock markets
The Effect of Biochar and Straw Return on N<sub>2</sub>O Emissions and Crop Yield: A Three-Year Field Experiment
To evaluate the effects of application of biochar and straw return for consecutive years on N2O emissions and crop yields in North China, a three-year field experiment of applying biochar and straw following a ten-year application was conducted in a wheat–maize rotation system. Four treatments were set up, including F (NPK fertilizer only); FB (NPK fertilizer + 9.0 t·ha−1 biochar); FS (NPK fertilizer + straw); and FSB ((NPK fertilizer + 9.0 t·ha−1 biochar combined with straw). The results showed that compared with the F treatment, the FB treatment significantly reduced soil N2O emissions by 20.2%, while the FS and FSB treatments increased it by 23.7% and 41.4%, respectively. The FB treatment reduced soil N2O emissions by 15.1% in the wheat season and 23.2% in the maize season, respectively. The FS and FSB treatments increased the N2O emissions by 20.7% and 36.7% in the wheat season, respectively, and by 25.5% and 44.2% in the maize season, respectively. In the wheat season, the soil water content (SWC), NO3−-N content and pH were the main influencing factors of the soil N2O emissions. In the maize season, SWC and NO3−-N content were the main influencing factors. In addition, the FB, FS and FSB treatments increased the crop yield by 4.99%, 8.40% and 10.25% compared with the F treatment, respectively. In conclusion, consecutive application of biochar can significantly reduce N2O emissions and improve crop yield. Although FS and FSB treatments can also improve the crop yield, they are not beneficial to suppressing N2O emissions. Therefore, the successive application of biochar is an effective measure to reduce N2O emissions and maintain crop yield
- …