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<jats:p>Ring artifacts will happen mostly when the detector has inconsistent response among the detector channels, and the characteristic produced rings centered in the iso-center in the reconstructed slices inevitably affect the recognition and analysis of the corresponding sample structures in neutron computed tomography (CT). In this work, a ring correction method based on the projection-field (RCP) is proposed, it is a pre-processing method and provides the corrected projection data directly, which is also conducive to efficient data storage and other algorithmic researches. Simulation and physical experiments are performed for verifying the effect of the method, and one of the correction methods based on the image-field is used for comparison. The results demonstrate that the RCP can correct the ring artifacts well without reducing the image resolution or over-correction.</jats:p>

<jats:p>To improve the signal to noise ratio (SNR) and the short-term stability of cesium atomic fountain clocks, the work of two-laser optical pumping is presented theoretically and experimentally. The short-term stability of the NIM6 fountain clock has been improved by preparing more cold atoms in the | <jats:italic>F</jats:italic> = 4, <jats:italic>m<jats:sub>F</jats:sub> </jats:italic> = 0〉 clock state with a shortened cycle time. Two <jats:italic>π</jats:italic>-polarized laser beams overlapped in the horizontal plane have been applied after launching, one is resonant with | <jats:italic>F</jats:italic> = 4〉 → | <jats:italic>F</jats:italic>′ = 4〉 transition and the other is resonant with | <jats:italic>F</jats:italic> = 3〉 → | <jats:italic>F</jats:italic>′ = 4〉 transition. With optical pumping, the population accumulated in the | <jats:italic>m<jats:sub>F</jats:sub> </jats:italic> = 0〉 clock state is improved from 11% to 63%, and the detection signal is increased by a factor of 4.2, the SNR of the clock transition probability and the short-term stability are also improved accordingly.</jats:p>

<jats:p>We report construction of an iodine-stabilized laser frequency standard at 532 nm based on modulation transfer spectroscopy (MTS) technology with good reproducibility. A frequency stability of 2.5 × 10<jats:sup>−14</jats:sup> at 1 s averaging time is achieved, and the frequency reproducibility has a relative uncertainty of 3.5 × 10<jats:sup>−13</jats:sup>, demonstrating the great stability of our setup. The systematic uncertainty of the iodine-stabilized laser frequency standard is evaluated, especially the contribution of the residual amplitude modulation (RAM). The contribution of the RAM in MTS cannot be evaluated directly. To solve this problem, we theoretically deduce the MTS signal with RAM under large modulation depth, and prove that the non-symmetric shape of the MTS signal is directly related to the MTS effect. The non-symmetric shape factor <jats:italic>r</jats:italic> can be calibrated with a frequency comb, and in real experiments, this <jats:italic>r</jats:italic> value can be obtained by least-squares fitting of the MTS signal, from which we can infer the RAMinduced frequency shift. The full frequency uncertainty is evaluated to be 5.3 kHz (corresponding to a relative frequency uncertainty of 9.4 × 10<jats:sup>−12</jats:sup>). The corrected transition frequency has a difference from the BIPM-recommended value of 2 kHz, which is within 1 <jats:italic>σ</jats:italic> uncertainty, proving the validity of our evaluation.</jats:p>

<jats:p>The phase transition behaviors of the shocked water are investigated by employing an optical transmittance <jats:italic>in-situ</jats:italic> detection system. Based on the light scattering theory and phase transformation kinetics, the phase transition mechanism of the water under multiple shocks is discussed. The experimental data indicate that the evolution of the transmittance of the shocked water can be broadly divided into three stages: relaxation stage, decline stage, and recovery stage. In the early stage of the phase transition, the new phase particles began to form around the quartz/window interface. It should be mentioned that the water/ice phase boundary seems to move toward the liquid region in one experiment of this work. Due to the new phase core being much smaller than the wavelength of the incident light, the transmittance of the sample within the relaxation stage remains steady. The decline stage can be divided into the rapid descent stage and the slow descent stage in this work, which is considered as the different growth rates of the new phase particle under different shock loadings. The recovery stage is attributed to the emergence of the new phase particles which are bigger than the critical value. However, the influence of the size growth and the population growth of the new phase particles on the transmittance restrict each other, which may be responsible for the phenomenon that the transmittance curve does not return to the initial level.</jats:p>

<jats:p>A type of Si-based blocked impurity band photoelectric detector with a planar architecture is designed and demonstrated by a modified silicon semiconductor processing technique. In this route, multiple ion implantation is utilized to ensure the uniform distribution of the P elements in silicon, and rapid thermal annealing treatment is used to activate the P atoms and reduce damages caused by ion-implantation. The fabricated prototype device exhibits an excellent photoelectric response performance. With a direct current (DC) bias voltage of –2.3 V, the device detectivity to blackbody irradiation is as high as 5 × 10<jats:sup>13</jats:sup>cm⋅Hz<jats:sup>1/2</jats:sup>/W, which corresponds to a device responsivity of nearly 4.6 A/W, showing their potential applications in infrared detection, infrared astrophysics, and extraterrestrial life science. In particular, the developed device preparation process is compatible with that for the CMOS-circuit, which greatly reduces the manufacturing cost.</jats:p>

<jats:p>Coating a glass monocapillary x-ray optics with high-density film is a promising way to improve transmission characteristics. For a long time, it has been a challenge to coat a high-density film in the inside of monocapillary with an extremely high length-to-diameter ratio. In this work, HfO<jats:sub>2</jats:sub> film is deposited on the inner wall of a tapered glass monocapillary with length 9.9 cm, entrance diameter 596.4 μm, and exit diameter 402.3 μm by atomic layer deposition. The coated and uncoated monocapillaries are studied by the transmission process of x-rays with energy from 5 keV to 100 keV and the x-ray fluorescence (XRF) spectra of a Mo sample are detected. Improved transmission characteristics have been obtained for the HfO<jats:sub>2</jats:sub>-coated monocapillary. The energy upper limit of focused x-rays increases from 18.1 keV to 33.0 keV and the ‘penetration halo’ is suppressed to some extent. The XRF spectrum presents two stronger peaks at ∼ 17.4 keV and ∼ 19.6 keV which are considered as the characteristic x-rays of Mo K<jats:sub> <jats:italic>α</jats:italic> </jats:sub> and Mo K<jats:sub> <jats:italic>β</jats:italic> </jats:sub>. These results reveal that more higher energy x-rays from the W x-ray tube are totally reflected on the inner wall of the HfO<jats:sub>2</jats:sub>-coated glass monocapillary due to the increase of total reflection critical angle. This work is significant for more applications of monocapillary in higher energy x-ray field.</jats:p>

<jats:p>Many terrestrial experiments have been designed to detect domain walls composed of axions or axionlike particles (ALPs), which are promising candidates of dark matter. When the domain wall crosses over the Earth, the pseudoscalar field of ALPs could couple to the atomic spins. Such exotic spin-dependent couplings can be searched for by monitoring the transient-in-time change of the atomic spin precession frequency in the presence of a magnetic field. We propose here a single-species cesium atomic comagnetometer, which measures the spin precession frequencies of atoms in different ground-state hyperfine levels, to eliminate the common-mode magnetic-field variations and search for the exotic non-magnetic couplings solely between protons and ALPs. With the single-species atomic comagnetometer, we experimentally rule out the possibility that the decay constant of the linear pseudoscalar couplings of ALPs to protons is <jats:italic>f</jats:italic> <jats:sub>p</jats:sub> ≲ 3.71 × 10<jats:sup>7</jats:sup> GeV. The advanced system has the potential to constrain the constant to be <jats:italic>f</jats:italic> <jats:sub>p</jats:sub> ≲ 10.7 × 10<jats:sup>9</jats:sup> GeV, promising to improve astrophysical constraint level by at least one order of magnitude. Our system could provide a sensitive detection method for the global network of optical magnetometers to search for exotic physics.</jats:p>

<jats:p>Accelerating materials discovery crucially relies on strategies that efficiently sample the search space to label a pool of unlabeled data. This is important if the available labeled data sets are relatively small compared to the unlabeled data pool. Active learning with efficient sampling methods provides the means to guide the decision making to minimize the number of experiments or iterations required to find targeted properties. We review here different sampling strategies and show how they are utilized within an active learning loop in materials science.</jats:p>

<jats:p>Combining first-principles accuracy and empirical-potential efficiency for the description of the potential energy surface (PES) is the philosopher’s stone for unraveling the nature of matter via atomistic simulation. This has been particularly challenging for multi-component alloy systems due to the complex and non-linear nature of the associated PES. In this work, we develop an accurate PES model for the Al–Cu–Mg system by employing deep potential (DP), a neural network based representation of the PES, and DP generator (DP-GEN), a concurrent-learning scheme that generates a compact set of <jats:italic>ab initio</jats:italic> data for training. The resulting DP model gives predictions consistent with first-principles calculations for various binary and ternary systems on their fundamental energetic and mechanical properties, including formation energy, equilibrium volume, equation of state, interstitial energy, vacancy and surface formation energy, as well as elastic moduli. Extensive benchmark shows that the DP model is ready and will be useful for atomistic modeling of the Al–Cu–Mg system within the full range of concentration.</jats:p>

<jats:p>Alkali-metal atomic magnetometers employing longitudinal carrier magnetic field have ultrahigh sensitivity to measure transverse magnetic fields and have been applied in a variety of precise-measurement science and technologies. In practice, the magnetometer response is not rigorously proportional to the measured transverse magnetic fields and the existing fundamental analytical model of this magnetometer is effective only when the amplitudes of the measured fields are very small. In this paper, we present a modified analytical model to characterize the practical performance of the magnetometer more definitely. We find out how the longitudinal magnetization of the alkali metal atoms vary with larger transverse fields. The linear-response capacity of the magnetometer is determined by these factors: the amplitude and frequency of the longitudinal carrier field, longitudinal and transverse spin relaxation time of the alkali spins and rotation frequency of the transverse fields. We give a detailed and rigorous theoretical derivation by using the perturbation-iteration method and simulation experiments are conducted to verify the validity and correctness of the proposed modified model. This model can be helpful for measuring larger fields more accurately and configuring a desirable magnetometer with proper linear range.</jats:p>