分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： We present a study of star-forming galaxies (SFGs) with pseudobulges (bulges with Sérsic index n 2σ) mean of specific star formation rate (sSFR) enhancement (sSFRenh = 0.33 ± 0.07 versus sSFRenh = 0.12 ± 0.06) and broader scatter (by ∼1 dex). The eight SFGs that have the highest sSFRenh in the sample all have pseudobulges. A majority (69%) of paired SFGs with strong enhancement (having sSFR more than 5 times the median of the control galaxies) have pseudobulges. The Spitzer data show that the pseudobulges in these galaxies are tightly linked to nuclear/circum-nuclear starbursts. Pseudobulge SFGs in S+S and in S+E pairs have significantly (>3σ) different sSFR enhancement, with the means of sSFRenh = 0.45 ± 0.08 and −0.04 ± 0.11, respectively. We find a decrease in the sSFR enhancements with the density of the environment for SFGs with pseudobulges. Since a high fraction (5/11) of pseudobulge SFGs in S+E pairs are in rich groups/clusters (local density N1Mpc ≥ 7), the dense environment might be the cause for their low sSFRenh.
分类： 核科学技术 >> 核科学与技术 提交时间： 2024-05-21
摘要： 神经网络可以基于大量数据学习输入输出变量之间的关系，具有强大的拟合能力，在包括核工程计算领域常用作程序的代理模型。中子输运计算作为中子学模拟的核心环节之一，其耗时较长的问题可以通过利用神经网络模型来解决。然而，神经网络模型具有一系列超参数需要设置，而手动调节这些超参数工作量大，重复繁琐，只能依靠经验进行，而且求解不同问题时这些超参数不可复用。为了解决以上问题，本文提出了一种采用贝叶斯优化(Bayesian Optimization)算法来调节神经网络超参数，结合了学习率衰减、损失函数优化方法，它可以针对不同问题的数据集，自动搜索超参数的最佳组合，以获得最佳性能，具有很高的灵活性和效率，泛化性强。本文对 TAKEDA基准题得到的堆芯关键参数进行拟合，结果表明有效增殖因数keff的平均误差在150pcm以内，TAKEDA1数据集上区域积分通量Φ的平均误差率为1.72%，最大误差率为7.56%。该研究可为人工智能在堆芯物理计算理论的应用提供一定参考。
分类： 核科学技术 >> 粒子加速器 提交时间： 2024-05-20
摘要： 电子辐照在核技术应用产业中成为重要的一部分，低能电子束在废水处理、食品保鲜等方面应用越来越广，辐照的计量参数对于辐照质量至关重要。由于低于300keV的电子束剂量学相关标准尚未建立，参数测量都溯源至10MeV电子直线加速器，测量对象的不一致带来了系统性的偏差。本论文针对低于300keV的低能电子，开展了测试与模拟计算相结合的电子束能量测量方法研究，研制了基于量热法的吸收剂量测量装置，探究了吸收剂量与束流强度、位移速度等参数的关系。结果表明：通过阶梯叠层法剂量实验结合能量沉积曲线模拟的方式实现了低能电子能量参数的测量，通过量热法实现了低能电子吸收剂量参数的测量，测量不确定度为11%（k=2）。本研究为低能电子辐照工艺提供了可靠的计量保障。
分类： 图书馆学、情报学 >> 情报学 提交时间： 2024-05-23
摘要： The Bradford’s law of bibliographic scattering is a fundamental law in bibliometrics and can provide valuable guidance to academic libraries in literature search and procurement. However, the Bradford’s curves can take various shapes at different time points and there is still a lack of causal explanation for it, so the prediction of its shape is still an open question. This paper attributes the deviation of Bradford curve from the theoretical J-shape to the integer constraints of the journal number and article number, and extends the Leimkuhler and Egghe’s formula to cover the core region of very productive journals, where the theoretical journal number of which fall below one, ftXi=CXiα . The key parameters of the extended formula are identified and studied by using the Simon-Yule model. The reasons for the Groos Droop are explained and the critical point for the shape change are studied. Finally, the proposed formulae are validated with the empirical data found in the literature. It is found that the proposed method can be used to predict the evolution of Bradford’s curves and thus guide the academic library for scientific literature procurement and utilization.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Owing to the broad energy coverage of Insight-HXMT in the hard X-ray band, we detected the highest energy of pulsation exceeding 200 keV around the 2017–2018 outburst peak of the first Galactic pulsating ultraluminous X-ray source (PULX) Swift J0243.6+6124, which is the highest energy detected from PULXs to date. We also obtained the highest energy of pulsation of every exposure during the outburst in 2017–2018, and found the highest energy is roughly positively correlated with luminosity. Using our newly developed method, we identified the critical luminosity being 4 × 1038 erg s−1 when the main peaks of the low and high energy pulse profiles became aligned, which separates the fan-beam dominated and pencil-beam dominated accretion regimes. Above the critical luminosity, the phase of the main peak shifted gradually from 0.5 to 0.8 until the outburst peak in all energy bands is reached, which is in agreement with the phase shift found previously at low energies. Our result is consistent with what is derived from spectral analysis.
分类： 天文学 >> 天文学 提交时间： 2024-05-24 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： The origin of intermediate helium (He)-rich hot subdwarfs is still unclear. Previous studies have suggested that some surviving Type Ia supernovae (SNe Ia) companions from the white dwarf + main-sequence (WD+MS) channel may contribute to the intermediate He-rich hot subdwarfs. However, previous studies ignored the impact of atomic diffusion on the post-explosion evolution of surviving companion stars of SNe Ia, leading to the aspect that they could not explain the observed surface He abundance of intermediate He-rich hot subdwarfs. In this work, by taking the atomic diffusion and stellar wind into account, we trace the surviving companions of SNe Ia from the WD+MS channel using the one-dimensional stellar evolution code MESA until they evolve into hot subdwarfs. We find that the surface He-abundances of our surviving companion models during their core He-burning phases are in a range of , which are consistent with those observed in intermediate He-rich hot subdwarfs. This seems to further support the notion that it is possible for surviving companions of SNe Ia in the WD+MS channel to form some intermediate He-rich hot subdwarfs.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Electromagnetic spins, including longitudinal and transverse ones, have been playing important roles in light-matter interactions. Here, we formulate a unified equation to uncover the physical origins and topological properties of longitudinal and transverse spins in a generic electromagnetic field. The equation reveals universally that the transverse spin is locked with the kinetic momentum and originated from the transverse inhomogeneities of field, whereas the helix-dependent longitudinal spin orients parallel to the local wavevector. Remarkably, a hidden extraordinary helix-dependent transverse spin possessing helix-dependent spin-momentum locking is discovered and the number of locking states consistent with the nontrivial topological spin Chern number. Furthermore, this spin which determines the inverted helical components is related to the Berry curvature closely. The findings, which are demonstrated experimentally by measuring the three-dimensional spin components in the focusing configuration, will deepen the understanding the underlying physics of spins and open an avenue for chiral quantum optical applications.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Polarization vectors of light traveling in a coiled optical fiber rotate around its propagating axis even in the absence of birefringence. This rotation was usually explained due to the Pancharatnam-Berry phase of spin-1 photons. Here, we use a purely geometric method to understand this rotation. We show that similar geometric rotations also exist for twisted light carrying orbital angular momentum (OAM). The corresponding geometric phase can be applied in photonic OAM-state-based quantum computation and quantum sensing.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Optical forces in the near fields have important applications in on-chip optical manipulations of small particles and molecules. Here, we report a study of optical force and torque on small particles induced by the optical polarization singularities of a gold cylinder. We show that the scattering of the cylinder generates both electric and magnetic C lines (i.e., lines of polarization singularities) in the near fields, and the C lines can induce complex force and torque on a dielectric/magnetic particle. The force and torque manifest dramatic spatial variations with interesting symmetry properties, providing rich degrees of freedom for near-field optical manipulations. The study, for the first time to our knowledge, uncovers the effect of optical polarization singularities on light-induced force and torque on small particles. The results contribute to the understanding of chiral light-matter interactions and can find applications in on-chip optical manipulations and optical sensing.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： How migratory birds can find the right way in navigating over thousand miles is an intriguing question, which much interested researchers in both fields of biology and physics for centuries. There several putative proposals that sound intuitively plausible all remain contested so far because those hypothesis-models of magnetoreceptor to sense geomagnetic field need either extremely high sensitivity or humankind-like intelligence to guide. Here we explore theoretically that the birds can navigate to their destination through an entirely new scenario to sense the geomagnetic field. Our proposal is based on separate peaks of the resonance-fluorescence spectrum of a four-level system derived from the ferric sulfide cluster which exists in a protein complex (Drosophila CG8198) of migratory birds. As the separation of spectral peaks contains information about geomagnetic field at both current location and birthland, the change of such separation cues the bird to choose a right direction to move and double-resonance emerges once arrived the destination. Our theoretical mechanism can explain previous experiments on the disorientation of migratory birds caused by oscillating magnetic field naturally and more precisely. This work provides insight to explain migratory navigation and motivates possible manmade practical devices.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Narrow linewidth laser(NLL) of high frequency stability and small form factor is essential to enable applications in long range sensing, quantum information and atomic clocks. Various high performance NLL have been demonstrated by Pound-Drever Hall(PDH) lock or self injection lock(SIL) of a seed laser to a vaccum-stabilized FP cavity of ultrahigh quality factor(Q). However they are often complicated lab setups due to the sophisticated stabilizing system and locking electronics. Here we report a compact NLL of 68mL volume, realized by SIL of a diode laser to a miniature FP cavity of 7.7x108 Q and 0.5mL volume, bypassing table-size vaccum, thermal and vibration isolation. We characterized the NLL with a self-delayed heterodyne system, the Lorentzian linewidth reaches 60mHz, and the integrated linewidth is ~80Hz. The frequency noise performance exceeds that of commercial NLLs and the best reported hybrid-integrated NLL realized by SIL to high Q on-chip ring resonators. Our work marks a major step toward a field-deployable NLL of superior performance utilizing ultra-high Q FP cavity.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Conventional coherent absorption occurs only when two incident beams exhibit mirror symmetry with respect to the absorbing surface, i.e., the two beams have the same incident angles, phases, and amplitudes. In this work, we propose a more general metasurface paradigm for coherent perfect absorption, with impinging waves from arbitrary asymmetric directions. By exploiting excitation of unidirectional evanescent waves, the output can be fixed at one reflection direction for any amplitude and phase of the control wave. We show theoretically and confirm experimentally that the relative amplitude of the reflected wave can be tuned continuously from zero to unity by changing the phase difference between the two beams, i.e. switching from coherent perfect absorption to full reflection. We hope that this work will open up promising possibilities for wave manipulation via evanescent waves engineering with applications in optical switches, one-side sensing, and radar cross section control.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Lingya Yu
Zengbo Wang
Lizhou Xu
Liyang Yue
Bing Yan
Igor V. Minin
Oleg V. Minin
Baidong Wu
Yiduo Chen
摘要： Photonic hook (PH) is a new type of artificial self-bending beam focused by a dielectric particle-lens with a curved waist smaller than the wavelength, which has the potential to revolutionize mesoscale photonics in many applications, e.g., optical trapping, signal switching, imaging, etc. In this paper, we discover a new mechanism that the highly curved PHs can be realised by the light interaction with the fully or partially metal-coated microchannels. The generated W-shaped and J-shaped PHs have bending angles exceeding 80-degree. Compared to other PH setups, the proposed design has a larger range to flexibly control the bending angle through the coating process and can be easily integrated with the established microfluidic systems.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： We show that the time-averaged Poynting vector in parity-time (PT ) symmetric coupled waveguides is always positive and cannot explain the stopped light at exceptional points (EPs). In order to solve this paradox, we must accept the fact that the fields E and H and the Poynting vector in non-Hermitian systems are in general complex. Based on the original definition of the instantaneous Poynting vector, a formula on the group velocity is proposed, which agrees perfectly well with that calculated directly from the dispersion curves. It explains not only the stopped light at EPs, but also the fast-light effect near it. This investigation bridges a gap between the classic electrodynamics and the non-Hermitian physics, and highlights the novelty of non-Hermitian optics.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Mode-locked lasers, which produce ultrashort pulses in the picosecond and femtosecond range, have enabled some of the most precise measurements. However, despite significant recent progress, resolving the temporal behavior of their short pulses is still a challenge. State-of-the-art oscilloscopes with tens of picosecond resolution prevent time-resolved observations in mode-locked lasers and limit the real-time pulse evolution tracking of ultrafast lasers. Here, using the time-lens technique with a Raman amplifier, we implement an ultrafast single-shot time-microscope (TM) with a high temporal magnification factor of 355 and a time measurement window of 1 millisecond that contains ~1.8*10^4 consecutive pulses. We use this TM to characterize the temporal evolution of mode-locked lasers and reveal a temporal sideway oscillation (winding) behavior, a previously unobserved feature of lasers in both theory and experiment. Our experimental observations confirm that the winding behavior is an essential feature in the operation of mode-locked lasers. We theoretically and experimentally found that the winding characteristic evolution originates from gain-induced fluctuations for relatively high gain energies, while Q-switched modulations being the main cause for lower energies. Our findings based on advanced real-time measurements open up new insights into ultrafast and transient optics and may impact future laser designs, modern ultrafast diagnostics, and influence progress in nonlinear optics in general.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Halide perovskite materials raised tremendous interest in recent years since their cheap fabrication, superior performance in both solar cell and light emitting diode (LED). Due to the existence of layered quantum well structure, quasi two-dimensional(2D) halide perovskite has more intriguing spin related physics than its 3D counterpart. For instance, the detection and brightening of dark exciton (DX) in 2D halide perovskite attracts much attention since these species can be used in opto-spintronic and quantum computing devices. Here, we report the gradually brightened emission of the DX at 2.33 eV with the thickness decreases in (PEA)2PbI4 single crystalline nanoflake, which hitherto has not been reported. By coupling with in-plane (IP) magnetic field in Voigt configuration, the DX emission can be sharply enhanced, while for the out-of-plane (OP) magnetic field in Faraday configuration, the DX emission has no noticeable change, which can be reconciled with the theory interpretation of magnetic field dependent wave function mixing between the four exciton states fi1, fi2, fi3- , fi3+. The emission of DX fi2 at 2.335 eV and the fine splitting of all the four states are observed in static PL spectroscopy for the first time. Our work thus clarifies the debating questions regarding to previous research on DX behavior in 2D halide perovskite material and sheds light on the road of realizing opto-spintronic or quantum computing devices with these materials.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Traditional lasers function using resonant cavities, in which the round-trip optical path is exactly equal to an integer multiple of the intracavity wavelengths to constructively enhance the spontaneous emission rate. By taking advantage of the enhancement from the resonant cavity, the narrowest sub-10-mHz-linewidth laser and a $10^{-16}$-fractional-frequency-stability superradiant active optical clock (AOC) have been achieved. However, a laser with atomic spontaneous radiation being destructively inhibited in an anti-resonant cavity, where the atomic resonance is exactly between two adjacent cavity resonances, has not been reported. Herein, we experimentally demonstrate inhibited stimulated emission and termed it an inhibited laser. Compared with traditional superradiant AOCs, which exhibit superiority in terms of the high suppression of cavity noise, the suppression of the cavity-pulling effect of an inhibited laser can be further improved by a factor of $(2F/pi)^2$, i.e., 2.07 in this work, which was improved from 26 to 53 times. This study will guide further development of AOCs with better stability, and thus, it is significant for quantum metrology and may lead to new research in the laser physics and cavity quantum electrodynamics fields.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： In many-cycle plane waves at intermediate intensities, the nonlinear trident process can be well-approximated by the two sequential steps of nonlinear Compton scattering of a polarised real photon followed by its transformation into an electron-positron pair via nonlinear Breit-Wheeler pair creation. We investigate this two-step process in the intermediate intensity regime by employing the locally monochromatic approximation for each step and numerically evaluating resulting expressions. When photon polarisation is included, it is found to produce an order 10% decrease in the trident rate: the importance of polarisation increases at lower intensities, and decreases at higher intensities. Its importance persists at higher intensities in a linearly-polarised background, but disappears at high intensities in a circularly-polarised background. If the two steps are made to take place in two linearly-polarised plane wave pulses with perpendicular polarisations, the pair yield can be increased by approximately 30% compared to two plane waves with the same polarisation. It is also shown that harmonic structures in the Compton step can be passed to the pair step if the Compton edge is at an energy of the order of the threshold for linear Breit-Wheeler.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Resampling by interpolation is the traditional method to process sample in nonunform sampling Fourier transform spectrometer. Nonuniform discrete Fourier transform is an alternative to interpolation that has not been overlooked before. With the aid of experiment, we systematically compare the NUFFT method with resampling by interpolation FFT method in nonuniform sampling Fourier transform spectrometer. We found that NUFFT is comparable to interpolation in spectral profile and spectral noise levels and is better in spectral amplitudes. We also found that It has significant advantage in under-sampling and anti-aliasing property which is offered by the unique non-periodic nature of nonuniform sampling. It is faster and consumes less computer memory in our python implementation. Overall, we found that NUFFT is superior to traditional interpolation method with mostly better performances as well as additional capabilities.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Xiao Sun
Song Liang
Weiqing Cheng
Shengwei Ye
Yiming Sun
Yongguang Huang
Ruikang Zhang
Jichuan Xiong
Xuefeng Liu
John H. Marsh
Lianping Hou
摘要： We report an AlGaInAs multiple quantum well integrated source of polarization controlled light consisting of a polarization mode converter PMC, differential phase shifter(DPS), and a side wall grating distributed-feedback DFB laser. We demonstrate an asymmetrical stepped-height ridge waveguide PMC to realize TE to TM polarization conversion and a symmetrical straight waveguide DPS to enable polarization rotation from approximately counterclockwise circular polarization to linear polarization. Based on the identical epitaxial layer scheme, all of the PMC, DPS, and DFB laser can be integrated monolithically using only a single step of metalorganic vapor phase epitaxy and two steps of III V material dry etching. For the DFB-PMC device, a high TE to TM polarization conversion efficiency 98% over a wide range of DFB injection currents is reported at 1555 nm wavelength. For the DFB-PMC-DPS device, a 60 degree rotation of the Stokes vector was obtained on the Poincar\'e sphere with a range of bias voltage from 0 V to -4.0 V at IDFB is 170 mA.
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