Detecting Abrupt Change of Channel Covariance Matrix in IRS-Assisted Communication

The knowledge of channel covariance matrices is crucial to the design of intelligent reflecting surface (IRS) assisted communication. However, channel covariance matrices may change suddenly in practice. This letter focuses on the detection of the above change in IRS-assisted communication. Specifically, we consider the uplink communication system consisting of a single-antenna user (UE), an IRS, and a multi-antenna base station (BS). We first categorize two types of channel covariance matrix changes based on their impact on system design: Type I change, which denotes the change in the BS receive covariance matrix, and Type II change, which denotes the change in the IRS transmit/receive covariance matrix. Secondly, a powerful method is proposed to detect whether a Type I change occurs, a Type II change occurs, or no change occurs. The effectiveness of our proposed scheme is verified by numerical results.Comment: accepted by IEEE Wireless Communications Letter

AT2023lli: A Tidal Disruption Event with Prominent Optical Early Bump and Delayed Episodic X-ray Emission

High-cadence, multiwavelength observations have continuously revealed the diversity of tidal disruption events (TDEs), thus greatly advancing our knowledge and understanding of TDEs. In this work, we conducted an intensive optical-UV and X-ray follow-up campaign of TDE AT2023lli, and found a remarkable month-long bump in its UV/optical light curve nearly two months prior to maximum brightness. The bump represents the longest separation time from the main peak among known TDEs to date. The main UV/optical outburst declines as $t^{-4.10}$, making it one of the fastest decaying optically selected TDEs. Furthermore, we detected sporadic X-ray emission 30 days after the UV/optical peak, accompanied by a reduction in the period of inactivity. It is proposed that the UV/optical bump could be caused by the self-intersection of the stream debris, whereas the primary peak is generated by the reprocessed emission of the accretion process. In addition, our results suggest that episodic X-ray radiation during the initial phase of decline may be due to the patched obscurer surrounding the accretion disk, a phenomenon associated with the inhomogeneous reprocessing process. The double TDE scenario, in which two stars are disrupted in sequence, is also a possible explanation for producing the observed early bump and main peak. We anticipate that the multicolor light curves of TDEs, especially in the very early stages, and the underlying physics can be better understood in the near future with the assistance of dedicated surveys such as the deep high-cadence survey of the 2.5-meter Wide Field Survey Telescope (WFST).Comment: 14 pages, 8 figures,accepted for publication by ApJ

Change of Soil Carbon Fractions and Water-Stable Aggregates in a Forest Ecosystem Succession in South China

In order to evaluate the dynamics of carbon storage during forest succession and explore the significance of water relations and soil stability in forest environments, a study was conducted in 2011. This study investigated the dynamics of soil organic carbon (SOC) fractions and its protection through aggregation along the successional forests. An experiment in South China examined pine forest (PF), pine and broadleaved mixed forest (PBMF), and monsoon evergreen broadleaf forest (MEBF), which represent the early, middle, and advanced succession stages, respectively. Soil was sampled at 0–15, 15–30, 30–45, and 45–60 cm depths. We analyzed active, slow, and passive organic carbon, as well as particulate organic matter carbon (POM-C) and nitrogen (POM-N), and measured the weight and concentration of water-stable aggregates in four classes (>2000 μm, 250–2000 μm, 53–250 μm, and <53 μm). The results suggested that various carbon fractions and the percentage of active and passive carbon to total organic carbon (TOC) increased with forest succession. The percentage of water-stable aggregates in >2000 μm (0–15 cm and 15–30 cm) and <53 μm (45–60 cm) in MEBF was significantly higher than in PBMF and PF. The SOC content of all size classes of water-stable aggregates in 0–45 cm were significantly increased with forest succession. In conclusion, forest succession contributed to the accumulation of carbon storage, and the increasing percentage of silt- and clay-size (<53 μm) fraction improved the stability of soil organic matter (SOM)

A global dataset of plant available and unavailable phosphorus in natural soils derived by Hedley method

Soil phosphorus (P) fractions are critical for understanding soil P dynamics and availability. This paper provides a global dataset of soil P fractions separated by the Hedley method. The dataset also includes key environmental factors associated with soil P dynamics and availability, including climate factors, vegetation, soil and parent material types, soil age, and soil physiochemical properties such as particle size, bulk density, pH in water, organic carbon, total nitrogen, and extractable iron and aluminium concentrations. This dataset includes measures of Hedley P fractions of 802 soil samples and was gathered through a literature survey of 99 published studies. Plant availability of each soil P fraction was noted. We anticipate that the global dataset will provide valuable information for studying soil P dynamics and availability, and it will be fused into earth system models to better predict how terrestrial ecosystems will respond to global environmental changes

A Novel Approach for Evaluating the Contraction of Hypo-Peritectic Steels during Initial Solidification by Surface Roughness

The contraction of peritectic steels in the initial solidification has an important influence on the formation of surface defects of continuously cast slabs. In order to understand the contraction behavior of the initial solidification of steels in the mold, the solidification process and surface roughness in a commercial hypo-peritectic and several non-peritectic steels were investigated using Confocal Scanning Laser Microscope (CSLM). The massive transformation of delta-Fe (δ) to austenite (γ) was documented in the hypo-peritectic steel, which caused surface wrinkles and greatly increases the surface roughness of samples in the experiments. Surface roughness (Ra(δ→γ)) was calculated to evaluate the contraction level of the hypo-peritectic steel due to δ–γ transformation. The result shows that the surface roughness method can facilitate the estimation of the contraction level of peritectic transformation over a wide range of cooling rates

Study of the Effect of Carbon on the Contraction of Hypo-Peritectic Steels during Initial Solidification by Surface Roughness

In the continuous casting process, the shrinkage of the peritectic phase transition during the initial solidification process has an important influence on the surface quality of peritectic steel. The initial solidification process of 0.10C%, 0.14C%, and 0.16C% peritectic steels was observed in situ by a high temperature laser confocal microscope, and the contraction degree during initial solidification was characterized by surface roughness. The results showed that under the cooling rate of 20 °C/s, the surface roughness value Ra(δ/γ) of 0.10C% peritectic steel was 32 μm, the Ra(δ/γ) value of 0.14C% peritectic steel was 25 μm, and the Ra(δ/γ) value of 0.16C% peritectic steel was 17 μm. With increasing carbon content, the contraction degree of the δ→γ transformation decreased, and the value of the surface roughness Ra(δ/γ) declined. Therefore, surface roughness can characterize the contraction degree of the δ→γ transformation in the initial solidification process of peritectic steel under the condition of a large cooling rate

Nitrogen deposition influences nitrogen isotope composition in soil and needles of Pinus massoniana forests along an urban-rural gradient in the Pearl River Delta of south China

Purpose: Atmospheric nitrogen (N) deposition remains globally and regionally a significant N source in forest ecosystems, with intensive industrial activities. Stable N isotope ratio (δN) is a useful indicator widely adopted to assess environmental and ecological impacts of anthropogenic N inputs. On the basis of temporal changes in tree ring δN established recently, the present study investigated the influence of N deposition on δN in needles of Masson pine (Pinus massoniana L.) and forest soil along an urban-rural gradient in the Pearl River Delta of south China. Materials and methods: Soil and needle samples were selected from South China Botanical Garden (SBG) in Guangzhou, Ding Hu Shan Natural Reserve (DHS) in Zhaoqing, and Nan Kun Shan Natural Reserve (NKS) in Huizhou. Five soil profiles at each site were sampled at three horizons: organic horizon (Oa), 0-10 and 10-20 cm depths, underneath the selected Masson pine trees. Soil samples were air-dried and sieved through 2 mm for analysis. Current-year and previous-year needles of Masson pine were collected from outer branches of the middle canopy at south, west, east, and north directions, and pooled according to needle age for each tree. Needles were rinsed, dried, ground, and stored in desiccator before analysis. Nitrogen isotope ratios were determined by Finnigan isotope mass spectrometer. Results and discussion: Significant differences in soils (Oa and 0-10 cm depth layers) and needles along the urban-rural gradient were revealed with positively high δN values (+2.19 ± 1.43‰ in Oa, +6.67 ± 1.52‰ in 0-10 cm depth layer and about +1.0‰ in needles) at the rural site (NKS) and negatively low δN values (-5.51 ± 1.38‰ in Oa, -1.11 ± 1.36‰ in 0-10 cm depth layer and about -5.0‰ in needles) at the highest N deposition site (SBG). Needles exposed to high N deposition had significantly different δN values between age classes. The results suggested that atmospheric N deposition density contributed to the patterns of δN in soil and needles of Pinus massoniana along the urban-rural gradient. Conclusions: The detectably decreasing trends of δN observed in the soils and pine needles from NKS to SBG implied that N deposition has influenced the forests N isotope composition. The patterns of soil- and needle-δN of Masson pine might be closely related to N deposition intensity. Values of δN in soils and needles were indicative of the gradient of urban-rural N deposition in the Pearl River Delta of south China