Abstract To investigate gamma-ray bursts (GRBs) in depth, it is crucial to develop an effective method for identifying GRBs accurately. Current criteria, e.g., onboard blind search, ground blind ...search, and target search, are limited by manually set thresholds and perhaps miss GRBs, especially for subthreshold events. We proposed a novel approach that utilizes convolutional neural networks (CNNs) to distinguish GRBs and non-GRBs directly. We structured three CNN models, plain -CNN, ResNet, and ResNet-CBAM, and endeavored to exercise fusing strategy models. Count maps of NaI detectors on board Fermi/Gamma-ray Burst Monitor were employed, as the input samples of data sets and models were implemented to evaluate their performance on different timescale data. The ResNet-CBAM model trained on the 64 ms data set achieves high accuracy overall, which includes residual and attention mechanism modules. The visualization methods of Grad-CAM and t-SNE explicitly displayed that the optimal model focuses on the key features of GRBs precisely. The model was applied to analyze 1 yr data, accurately identifying approximately 98% of GRBs listed in the Fermi burst catalog, eight out of nine subthreshold GRBs, and five GRBs triggered by other satellites, which demonstrated that the deep-learning methods could effectively distinguish GRBs from observational data. Besides, thousands of unknown candidates were retrieved and compared with the bursts of SGR J1935+2154, for instance, which exemplified the potential scientific value of these candidates indeed. Detailed studies on integrating our model into real-time analysis pipelines thus may improve their accuracy of inspection and provide valuable guidance for rapid follow-up observations of multiband telescopes.
ABSTRACT
We present 637 low-redshift optical spectra collected by the Berkeley Supernova Ia Program (BSNIP) between 2009 and 2018, almost entirely with the Kast double spectrograph on the Shane 3 m ...telescope at Lick Observatory. We describe our automated spectral classification scheme and arrive at a final set of 626 spectra (of 242 objects) that are unambiguously classified as belonging to Type Ia supernovae (SNe Ia). Of these, 70 spectra of 30 objects are classified as spectroscopically peculiar (i.e. not matching the spectral signatures of ‘normal’ SNe Ia) and 79 SNe Ia (covered by 328 spectra) have complementary photometric coverage. The median SN in our final set has one epoch of spectroscopy, has a redshift of 0.0208 (with a low of 0.0007 and high of 0.1921), and is first observed spectroscopically 1.1 d after maximum light. The constituent spectra are of high quality, with a median signal-to-noise ratio of 31.8 pixel−1, and have broad wavelength coverage, with $\sim\! 95{{\ \rm per\ cent}}$ covering at least 3700–9800 Å. We analyse our data set, focusing on quantitative measurements (e.g. velocities, pseudo-equivalent widths) of the evolution of prominent spectral features in the available early-time and late-time spectra. The data are available to the community, and we encourage future studies to incorporate our spectra in their analyses.
The determination of uranium isotopic composition in ultra-trace U samples is very important in different fields, especially for the nuclear forensics. A new Accelerator Mass Spectrometry (AMS) ...technique has been developed for the measurement of uranium isotopic ratios in ng level uranium samples at China Institute of Atomic Energy (CIAE). Recently, the method was further optimized and developed by using a series of blank and standard samples. The results show that the 236U at the femtogram level can be determined in nanogram U samples by the newly developed AMS technique at CIAE. The experimental setup, performances and results will be detailed in this contribution.
This work presents the first demonstration of the transistor-free memory-diode (MD) array fabricated on Ge-on-Insulator (GeOI), which can work as an ultra-compact <inline-formula> <tex-math ...notation="LaTeX">8{F}^{{2}} </tex-math></inline-formula> ternary content addressable memory (TCAM). Through the wafer bonding and thinning techniques, the Ge layer in the GeOI structure maintains the monocrystalline quality originated from bulk Ge to ensure the Fermi-level pinning effect, forming an effective Schottky barrier with low reverse-bias leakage currents. Furthermore, an ultra-thin Y-doped GeOx layer is introduced to suppress the surface-state current, enabling a higher rectifying ratio. Thanks to the ultra-high rectifying (<inline-formula> <tex-math notation="LaTeX">>\,\,2\times 10^{{5}}{)} </tex-math></inline-formula> and sufficient on/off ratios (> 500), the 4-bits MD-TCAM array shows over 2 orders differences between the match and mismatch currents, which experimentally verifies the feasibility and accuracy of parallel data search.
This study extracts UF
-
2
ions from UF
4
sample material for the first time so as to improve the measurement accuracy and sensitivity for accelerator mass spectrometry (AMS) measurement of
236
U. ...Compared to the commonly used UO
-
/UO
2
(or U
3
O
8
) combination, the UF
-
2
/UF
4
approach brings a higher beam current of extracted U-containing ions and lower interference from U isotopes (
235
U in particular). The UF
4
prepared with the procedures developed in this work can provide a higher ratio of F
-
/O
-
and therefore lower interference from O-containing
235
U and
238
U molecular ions, compared with that from the UF
4
made by conventional liquid-phase reaction. The AMS experiment was carried out on the AMS system at China Institute of Atomic Energy (CIAE), where only a simple surface barrier detector was used to record ions and a reference
236
U sample with a
236
U/
238
U ratio of 10
-10
was analyzed. The result shows that the measurement sensitivity of the UF
-
2
/UF
4
approach is lower than 10
-10
and that the reference
236
U sample result is in agreement with the reference value within the uncertainty limits, with the relative uncertainty only 4%. In comparison, the measurement sensitivity of the UO
-
/U
3
O
8
combination approach is 10
-9
, and it cannot give a concrete value for the same reference sample using the same AMS system. If the sophisticated 500-ps-resolution time-of-flight detection system is used in combination with the UF
-
2
/UF
4
approach, a sensitivity of 10
-13
(or lower) is expected.
The 239+240Pu and 137Cs activities and 240Pu/239Pu atom ratios in surface soil and soil core collected from Qinghai-Tibet Plateau were investigated. The maximum of 239+240Pu and 137Cs activity ...concentrations in five soil cores were found in upper layers and have a same trend: the maximum followed by exponential decline. The 240Pu/239Pu atom ratio ranged from 0.160 ± 0.009 to 0.212 ± 0.012, clarified that the plutonium mainly came from the global fallout and the contribution of Lop Nor test sites was negligible. In addition, the vertical profiles of radionuclides (210Pb, 238U, 232Th, 226Ra, 40K) have been studied and a high correlation has been found between them. The correlations of Pu between organic matter (OM) and heavy metals were also studied. Person Correlation Coefficients revealed Pu had significant positive correlations with organic matter and Cd, Cu, Co, Zn, but negative correlation with Tl. The results have important implication for further understanding of the sources, records and environmental impacts of global and regional nuclear activities, which expanded the database of Pu activity level and atom ratio in Chinese soil and established a foundation for future environmental risk assessment.
•239+240Pu activity in Qinghai soil was 0.01 ± 0.01 mBq/g-2.20 ± 0.15 mBq/g.•240Pu/239Pu atom ratio indicating that Pu mainly came from the global fallout.•Inventory of 239 + 240Pu in Qinghai was 116.57–554 Bq/m2.•Pu has positive correlations with OM, Cd, Co, Cu, Zn and negative with Tl.
In this work, we developed a nonvolatile ternary content addressable memory (TCAM) with a cell size of <inline-formula> <tex-math notation="LaTeX">0.01~\mu \text{m}^{{2}} </tex-math></inline-formula> ...utilizing the Ge-based memory diode (MD), which has the most area-efficient TCAM design reported. The MDs have a high current ratio between ON and OFF states and a large rectifying ratio, showing the potential usage in large-dimension TCAM arrays. Besides, the functionality of parallel search was demonstrated with a 2-bit MD-TCAM array by experiment, and the electrical characterization showed expected results. With the help of the sub-ns ultrafast measurement system, it is confirmed that the search energy of MD-TCAM could reach as low as 1.0 fJ/bit/mismatch, and one search operation can be performed within 200 ps. Furthermore, the circuit-level simulation results verified that the MD-TCAM developed in this study shows good performance in 128-bit parallel searching, which is promising for the ultrafast and low-power data search applications in the coming IoT era.
Tiankeng is a typical Karst relief of the late Quaternary Period. Studies on the exposure ages of Tiankeng are very important in geographical research to elucidate the formation condition, the ...developing process, and the features of biological species. 36Cl on the surface layer of the rupture cross-section of Tiankeng is largely produced by cosmogenic high-energy neutron induced reactions 40Ca(n, αp) and 39K(n, α), and has accumulated since the formation of the Tiankeng. Low-energy neutron reaction 35Cl(n, γ) contributes a small portion of 36Cl. In this work, the concentration of the cosmogenic 36Cl in rock samples taken from Dashiwei Tiankeng, Leye County, Guangxi Zhuang Autonomous Region, China, was measured jointly by Accelerator Mass Spectrometry (AMS) laboratories of CIAE and University of Tsukuba in an effort to estimate the formation time (or exposure age) of the Tiankeng. The results show that the exposure time of Da Shiwei Tiankeng is about 26±9.6ka (without erosion correction). The sampling strategy and procedures, experimental set-up, and preliminary results will be presented in detail.
ABSTRACT
We present BVRI and unfiltered light curves of 93 Type Ia supernovae (SNe Ia) from the Lick Observatory Supernova Search (LOSS) follow-up program conducted between 2005 and 2018. Our sample ...consists of 78 spectroscopically normal SNe Ia, with the remainder divided between distinct subclasses (3 SN 1991bg-like, 3 SN 1991T-like, 4 SNe Iax, 2 peculiar, and 3 super-Chandrasekhar events), and has a median redshift of 0.0192. The SNe in our sample have a median coverage of 16 photometric epochs at a cadence of 5.4 d, and the median first observed epoch is ∼4.6 d before maximum B-band light. We describe how the SNe in our sample are discovered, observed, and processed, and we compare the results from our newly developed automated photometry pipeline to those from the previous processing pipeline used by LOSS. After investigating potential biases, we derive a final systematic uncertainty of 0.03 mag in BVRI for our data set. We perform an analysis of our light curves with particular focus on using template fitting to measure the parameters that are useful in standardizing SNe Ia as distance indicators. All of the data are available to the community, and we encourage future studies to incorporate our light curves in their analyses.
In this work, BVRI light curves of 55 Type II supernovae (SNe II) from the Lick Observatory Supernova Search programme obtained with the Katzman Automatic Imaging Telescope and the 1 m Nickel ...telescope from 2006 to 2018 are presented. Additionally, more than 150 spectra gathered with the 3 m Shane telescope are published. We conduct an analyse of the peak absolute magnitudes, decline rates, and time durations of different phases of the light and colour curves. Typically, our light curves are sampled with a median cadence of 5.5 d for a total of 5093 photometric points. In average, V-band plateau declines with a rate of 1.29 mag (100 d)(exp −1), which is consistent with previously published samples. For each band, the plateau slope correlates with the plateau length and the absolute peak magnitude: SNe II with steeper decline have shorter plateau duration and are brighter. A time-evolution analysis of spectral lines in term of velocities and pseudo-equivalent widths is also presented in this paper. Our spectroscopic sample ranges between 1 and 200 d post-explosion and has a median ejecta expansion velocity at 50 d post-explosion of 6500 km s(exp −1) (H α line) and a standard dispersion of 2000 km s(exp −1). Nebular spectra are in good agreement with theoretical models using a progenitor star having a mass <16M⨀. All the data are available to the community and will help to understand SN II diversity better, and therefore to improve their utility as cosmological distance indicators.
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