Healable and conductive sulfur iodide for solid-state Li-S batteries.

Solid-state Li-S batteries (SSLSBs) are made of low-cost and abundant materials free of supply chain concerns. Owing to their high theoretical energy densities, they are highly desirable for electric vehicles1-3. However, the development of SSLSBs has been historically plagued by the insulating nature of sulfur4,5 and the poor interfacial contacts induced by its large volume change during cycling6,7, impeding charge transfer among different solid components. Here we report an S9.3I molecular crystal with I2 inserted in the crystalline sulfur structure, which shows a semiconductor-level electrical conductivity (approximately 5.9 × 10-7 S cm-1) at 25 °C; an 11-order-of-magnitude increase over sulfur itself. Iodine introduces new states into the band gap of sulfur and promotes the formation of reactive polysulfides during electrochemical cycling. Further, the material features a low melting point of around 65 °C, which enables repairing of damaged interfaces due to cycling by periodical remelting of the cathode material. As a result, an Li-S9.3I battery demonstrates 400 stable cycles with a specific capacity retention of 87%. The design of this conductive, low-melting-point sulfur iodide material represents a substantial advancement in the chemistry of sulfur materials, and opens the door to the practical realization of SSLSBs.

Particle-based hematite crystallization is invariant to initial particle morphology.

SignificanceMany crystallization processes occurring in nature produce highly ordered hierarchical architectures. Their formation cannot be explained using classical models of monomer-by-monomer growth. One of the possible pathways involves crystallization through the attachment of oriented nanocrystals. Thus, it requires detailed understanding of the mechanism of particle dynamics that leads to their precise crystallographic alignment along specific faces. In this study, we discover a particle-morphology-independent oriented attachment mechanism for hematite nanocrystals. Independent of crystal morphology, particles always align along the [001] direction driven by aligning interactions between (001) faces and repulsive interactions between other pairs of hematite faces. These results highlight that strong face specificity along one crystallographic direction can render oriented attachment to be independent of initial particle morphology.

Inorganic carbon is overlooked in global soil carbon research: A bibliometric analysis.

Soils are a major player in the global carbon (C) cycle and climate change by functioning as a sink or a source of atmospheric carbon dioxide (CO2). The largest terrestrial C reservoir in soils comprises two main pools: organic (SOC) and inorganic C (SIC), each having distinct fates and functions but with a large disparity in global research attention. This study quantified global soil C research trends and the proportional focus on SOC and SIC pools based on a bibliometric analysis and raise the importance of SIC pools fully underrepresented in research, applications, and modeling. Studies on soil C pools started in 1905 and has produced over 47,000 publications (>1.7 million citations). Although the global C stocks down to 2 m depth are nearly the same for SOC and SIC, the research has dominantly examined SOC (>96 % of publications and citations) with a minimal share on SIC (<4%). Approximately 40 % of the soil C research was related to climate change. Despite poor coverage and publications, the climate change-related research impact (citations per document) of SIC studies was higher than that of SOC. Mineral associated organic carbon, machine learning, soil health, and biochar were the recent top trend topics for SOC research (2020-2023), whereas digital soil mapping, soil properties, soil acidification, and calcite were recent top trend topics for SIC. SOC research was contributed by 151 countries compared to 88 for SIC. As assessed by publications, soil C research was mainly concentrated in a few countries, with only 9 countries accounting for 70 % of the research. China and the USA were the major producers (45 %), collaborators (37 %), and funders of soil C research. SIC is a long-lived soil C pool with a turnover rate (leaching and recrystallization) of more than 1000 years in natural ecosystems, but intensive agricultural practices have accelerated SIC losses, making SIC an important player in global C cycle and climate change. The lack of attention and investment towards SIC research could jeopardize the ongoing efforts to mitigate climate change impacts to meet the 1.5-2.0 °C targets under the Paris Climate Agreement of 2015. This bibliographic study calls to expand the research focus on SIC and including SIC fluxes in C budgets and models, without which the representation of the global C cycle is incomplete.

Structural Transformation in a Sulfurized Polymer Cathode to Enable Long-Life Rechargeable Lithium-Sulfur Batteries.

Sulfurized polyacrylonitrile (SPAN) represents a class of sulfur-bonded polymers, which have shown thousands of stable cycles as a cathode in lithium-sulfur batteries. However, the exact molecular structure and its electrochemical reaction mechanism remain unclear. Most significantly, SPAN shows an over 25% 1st cycle irreversible capacity loss before exhibiting perfect reversibility for subsequent cycles. Here, with a SPAN thin-film platform and an array of analytical tools, we show that the SPAN capacity loss is associated with intramolecular dehydrogenation along with the loss of sulfur. This results in an increase in the aromaticity of the structure, which is corroborated by a >100× increase in electronic conductivity. We also discovered that the conductive carbon additive in the cathode is instrumental in driving the reaction to completion. Based on the proposed mechanism, we have developed a synthesis procedure to eliminate more than 50% of the irreversible capacity loss. Our insights into the reaction mechanism provide a blueprint for the design of high-performance sulfurized polymer cathode materials.

High Nitrate Accumulation in the Vadose Zone after Land-Use Change from Croplands to Orchards.

Additional evidence indicates that the nitrate stored in the deep soil profile has an important role in regulating the global nitrogen (N) cycle. This study assessed the effects of land-use changes from croplands to intensive orchards (LUCO) on N surplus, nitrate accumulation in deep soil, and groundwater quality in the kiwifruit belt of the northern slope region of the Qinling Mountains, China. LUCO resulted in comparatively high N surplus in orchards (282 vs 1206 kg ha-1 yr-1, respectively). The average nitrate accumulation within the 0-10 m profiles of orchards was 7113 kg N ha-1, which was equal to approximately the total N surplus of 6 years of the orchards. The total nitrate stock within 0-10 m soil profiles of the kiwifruit belt was 266.5 Gg N, which was 3.5 times higher than the total annual N input. The nitrate concentrations of 97% of groundwater samples exceeded the WHO standard. The LUCO resulted in large nitrate storage in the vadose zone and caused serious contamination of groundwater. Our study highlights that nitrate accumulation in the vadose zone of an intensive land-use system is one of the main fates of surplus N and also a hotspot of nitrate accumulation.

CircFAT1 facilitates cervical cancer malignant progression by regulating ERK1/2 and p38 MAPK pathway through miR-409-3p/CDK8 axis.

Circular RNA FAT atypical cadherin 1 (circFAT1) has been reported to play vital roles in the progression of some cancers. However, the regulatory role and underlying mechanisms of circFAT1 in cervical cancer (CC) remain largely unknown. The expression of circFAT1, microRNA (miR)-409-3p and cyclin-dependent kinase 8 (CDK8) was detected using qRT-PCR and Western blot assays. Cell proliferation, apoptosis, migration and invasion in vitro were investigated using cell counting kit-8, colony formation, flow cytometry, and transwell assays, respectively. Western blot assay was used to determine the activation of ERK1/2 and p38 MAPK pathway. The interaction miR-409-3p and circFAT1 or CDK8 was confirmed by dual-luciferase reporter, pull-down or RIP assays. The effects of circFAT1 in vivo were determined using xenograft models. CircFAT1 was highly expressed in CC, and closely associated with poor prognosis. CircFAT1 knockdown resulted in the suppression of proliferation, migration and invasion, and promotion of apoptosis in CC cells via the inactivation of ERK1/2 and p38 MAPK pathway; also, circFAT1 silencing could inactivate this pathway and repressed CC tumor growth in vivo. Mechanistic analysis showed that circFAT1 directly sponged miR-409-3p and then relieved the repressive effect of miR-409-3p on its target CDK8. Furthermore, miR-409-3p inhibition reversed the effects of circFAT1 silencing on CC cells. Whereas, miR-409-3p overexpression impeded CC cell growth and motility, which was attenuated by CDK8. CircFAT1 promoted CC progression via activating ERK1/2 and p38 MAPK pathway through the miR-409-3p/CDK8 axis, suggesting a promising prognostic biomarker and therapeutic target for CC.

Counting-loss correction method based on dual-exponential impulse shaping.

Under the condition of high counting rate, the phenomenon of nuclear pulse signal pile-up using a single exponential impulse shaping method is still very serious, and leads to a severe loss in counting rate. A real nuclear pulse signal can be expressed as a dual-exponential decay function with a certain rising edge. This paper proposes a new dual-exponential impulse shaping method and shows its deployment in hardware to test its performance. The signal of a high-performance silicon drift detector under high counting rate in an X-ray fluorescence spectrometer is obtained. The result of the experiment shows that the new method can effectively shorten the dead-time caused by nuclear signal pile-up and correct the counting rate.

Facts to acidification-induced carbonate losses from Chinese croplands.

This letter explains the processes and mechanisms involved in the nitrogen-induced soil acidification causing substantial carbonate losses and subsequent CO2 emissions from Chinese croplands.

Dramatic loss of inorganic carbon by nitrogen-induced soil acidification in Chinese croplands.

Intensive crop production systems worldwide, particularly in China, rely heavily on nitrogen (N) fertilization, but left more than 50% of fertilizer N in the environment. Nitrogen (over) fertilization and atmospheric N deposition induce soil acidification, which is neutralized by soil inorganic carbon (SIC; carbonates), and carbon dioxide (CO2 ) is released to the atmosphere. For the first time, the loss of SIC stocks in response to N-induced soil acidification was estimated for Chinese croplands from 1980 to 2020 and forecasts were made up to 2100. The SIC stocks in croplands in 1980 were 2.16 Pg C (16.3 Mg C/ha) in the upper 40 cm, 7% (0.15 Pg C; 1.1 Mg C/ha) of which were lost from 1980 to 2020. During these 40 years, 7 million ha of cropland has become carbonate free. Another 37% of the SIC stocks may be lost up to 2100 in China, leaving 30 million ha of cropland (37.8%) without carbonates if N fertilization follows the business-as-usual (BAU) scenario. Compared to the BAU scenario, the reduction in N input by 15%-30% after 2020 (scenarios S1 and S2) will decrease carbonate dissolution by 18%-41%. If N input remains constant as noted in 2020 (S3) or decreases by 1% annually (S4), a reduction of up to 52%-67% in carbonate dissolution is expected compared to the BAU scenario. The presence of CaCO3 in the soil is important for various processes including acidity buffering, aggregate formation and stabilization, organic matter stabilization, microbial and enzyme activities, nutrient cycling and availability, and water permeability and plant productivity. Therefore, optimizing N fertilization and improving N-use efficiency are important for decreasing SIC losses from acidification. N application should be strictly calculated based on crop demand, and any overfertilization should be avoided to prevent environmental problems and soil fertility decline associated with CaCO3 losses.

CircZDHHC20 represses the proliferation, migration and invasion in trophoblast cells by miR-144/GRHL2 axis.

BACKGROUND: Preeclampsia (PE) is a prevalent pregnancy disorder that has been one of the leading causes of maternal and perinatal mortality worldwide. Circular RNAs (circRNAs) have recently considered as important regulators in PE pathogenesis. In the current study, we aimed to explore the impact and mechanisms of circRNA zinc finger DHHC-type palmitoyltransferase 20 (circZDHHC20) in PE pathogenesis. METHODS: RNase R assay and reverse transcription with Oligo(dT)18 primers were performed to confirm that circZDHHC20 was indeed circular transcript. The expression of circZDHHC20, grainyhead-like 2 (GRHL2) and miR-144 were assessed by quantitative real-time polymerase chain reaction (qRT-PCR). Subcellular localization assay was used to determine whether circZDHHC20 was predominantly present in the cytoplasm. The target correlations between miR-144 and circZDHHC20 or GRHL2 were confirmed using dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. Cell proliferation, migration, and invasion were detected by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetr-azolium (MTS), wound healing and transwell assays, respectively. Western blot was used for the quantification of GRHL2 protein level. RESULTS: Our data indicated that circZDHHC20 was up-regulated and miR-144 was down-regulated in PE placenta. CircZDHHC20 sequestered miR-144 by acting as a miR-144 sponge. CircZDHHC20 overexpression repressed trophoblast cell proliferation, migration, and invasion, while its knockdown exerted opposite effects. Moreover, miR-144 mediated the regulation of circZDHHC20 on trophoblast cell behaviors. GRHL2 was directly targeted and inhibited by miR-144. MiR-144 exerted regulatory effects on trophoblast cell proliferation, migration and invasion by GRHL2. Furthermore, circZDHHC20 modulated GRHL2 expression through sponging miR-144. CONCLUSION: Our study suggested that a high level of circZDHHC20 inhibited the proliferation, migration, and invasion in trophoblast cells at least partially through sponging miR-144 and up-regulating GRHL2, providing a novel mechanism of PE pathogenesis.

Do soil property variations affect dicyandiamide efficiency in inhibiting nitrification and minimizing carbon dioxide emissions?

Nitrification inhibitors (NIs) are used to retard the nitrification process and reduce nitrogen (N) losses. However, the effects of soil properties on NI efficacy are less clear. Moreover, the direct and indirect effects of soil property variations on NI efficiency in minimizing carbon dioxide (CO2) emissions have not been previously studied. An incubation experiment was conducted for 40 days with two treatments, N (200 mg N-urea kg-1) and N + dicyandiamide (DCD) (20 mg DCD kg-1), and a control group (without the N) to investigate the response of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to DCD application and the consequences for CO2, nitrous oxide (N2O) and ammonia (NH3) emissions from six soils from the Loess Plateau with different properties. The nitrification process completed within 6-18 days for the N treatment and within 30->40 days for the N + DCD treatment. AOB increased significantly with N fertilizer application, while this effect was inhibited in soils when DCD was applied. AOA was not sensitive to N fertilizer and DCD application. The nitrification rate was positively correlated with the clay (p < 0.05) and SOM contents (p < 0.01); DCD was more effective in loam soil with low SOM and high soil pH. Soil pH significantly was decreased with N fertilizer application, while it increased when DCD was applied. Moreover, DCD application decreased CO2 emissions from soils by 22%-172%; CO2 emissions were negatively correlated with the clay and SOM contents. DCD application decreased N2O emissions in each soil by 1.0- to 94-fold compared with those after N fertilizer application. In contrast, DCD application increased NH3 release from soils by 59-278%. NH3 volatilization was negatively correlated with clay (p < 0.05) and SOM (p < 0.01) contents and positively correlated with soil pH (p < 0.01). Therefore, soil texture, SOM and soil pH have significant effects on the DCD performance, nitrification process and gaseous emissions.

How much nitrogen does Africa need to feed itself by 2050?

Nitrogen (N) fertilizers are very important for global food self-sufficiency (FSS), particularly for Africa, where the N input in agriculture is very low. This is the first work which studies and calculates the amount of N fertilizer that each country in Africa needs to feed itself by 2050. In this study, we used five different scenarios of inorganic fertilizer N (IFN) use and human diets to calculate the amount of N fertilizer needed to achieve FSS in Africa by 2050 and analyze the changes in N budget; N losses and N use efficiency (NUE). These scenarios include 1) business as usual (BAU), 2) equitable diet (EqD; self-sufficiency), 3) an IFN input 20% less than the EqD (S1), 4) an IFN input 40% less than the EqD (S2), and 5) a 20% increase in IFN input relative to the EqD (S3). Under the BAU scenario, production trends continue as they have over the past five decades, including an unhealthy human diet. In the EqD scenario, the priority is to meet the local demand for both animal and plant proteins with a healthy human diet. Under the EqD scenario, increasing the total N input from 35 kg N ha-1 yr-1 to 181 kg N ha-1 yr-1 during 2016-2050 is needed to achieve FSS in Africa. This increase in N fertilizer use represents unprecedented N inputs to African terrestrial ecosystems - at least 52 Tg N yr-1 - which would lead to inevitable increases in N losses. We also found that the NUE would decrease from 63% during 2010-2016 to 50% by 2050, whereas the total N surplus would increase from 13 kg N ha-1 yr-1 to 90 kg N ha-1 yr-1 by 2050. The estimated gaseous emissions would increase from 8 kg N ha-1 yr-1 to 61 kg N ha-1 yr-1 by 2050. Our findings conclude that, it is very important to consider the high N losses in Africa if the EqD scenario is applied. The S1 and S2 scenarios result in much less environmental N loss, and better NUE compared with the EqD scenario. Therefore, based on these findings we can recommend the implementation of the S2 scenario with an IFN dose of 77 kg N ha-1 yr-1, in parallel with the use of modern agricultural techniques and the increased use of organic inputs.

Synthesis of 2D Hexagonal Hematite Nanosheets and the Crystal Growth Mechanism.

Nanostructure engineering of hematite is a promising strategy to overcome its performance limitations as a photodegradation catalyst for organic dyes or toxic organic chemicals. Precise control of exposed facets plays a vital role as an optimization strategy. Although great progress has been made in the synthesis of different crystal morphologies, design principles remain ad hoc, awaiting systematic control of facet expression within a clean synthesis protocol yielding versatile results. Herein, we report a simple method that enables precise morphology control to synthesize 2D hexagonal hematite nanosheets from two-line ferrihydrite. Nanosheet sizes and facet proportions were successfully tuned by changing the pH, the ratio of solvent ethanol to water, and the concentration of FeIII ions. The growth mechanism appears to involve a combination of ferrihydrite solid-state transformation and assembly into hematite, followed by an ion-by-ion growth that perfects the surface terminations. The finding helps to establish a rational basis for the design and optimization of hematite nanostructures.

Can secondary metabolites extracted from Moringa seeds suppress ammonia oxidizers to increase nitrogen use efficiency and reduce nitrate contamination in potato tubers?

Nitrification inhibition as an alleviation tool to decrease nitrogen (N) losses and increase N use efficiency (NUE) as well as reducing NO3- accumulation in plants is a promising technology. No study thus far has directly or indirectly to use the secondary metabolites extracted from Moringa (Moringa oleifera Lam) seeds as nitrification inhibitors. Moringa seed extract (MSE) was studied based on its content of phenolic compounds (PC) and for its antioxidant characteristic. A 2-year field experiment and 30-day incubation experiment were conducted with three treatments of control (CK), N fertilizer (300 kg N ha-1 and 200 mg N kg-1 soil for the field and incubation experiment, respectively), and N fertilizer with MSE (500 ppm as a TPC) to investigate the responses of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to MSE and the consequences for NUE and NO3- accumulation in potato tubers. Total phenolics amount was 144 mg gallic acid equivalent g-1 MSE, while flavonoid contents were 76.6 quercetin equivalent g-1 MSE. MSE showed antioxidant activity that was comparable to the standard antioxidants TBHQ and gallic acid. MSE application with N fertilizer retarded the nitrification process, as indicated by a higher NH4+-N and lower NO3--N content, compared with N fertilizer application alone. NH4+-N content reduced to initial CK level on Day 20 under N fertilizer application alone. However, NH4+-N content decreased to initial control level on Day 30 when MSE was applied. The mechanisms resulted from curbing AOB growth by phenolic compounds (TPC, TF, TAC), leading to a delay in nitrification process. AOB increased significantly when N fertilizer was applied alone; on the contrary, AOA was not sensitive to N fertilizer (with and without MSE). Increase in NUE from 37.5% to 66.3% in potato plants under MSE application with N fertilizer was also observed compared with N fertilizer application alone. The highest NO3- accumulation (569 mg NO3- kg-1) in tubers was recorded under N fertilizer application without MSE. MSE application significantly decreased NO3- accumulation (92 mg NO3- kg-1) in tubers which is lower than the maximum value of accepting tubers (200 mg NO3- kg-1). The highest average of N uptake, fresh and dry weight, carotenoids, chlorophyll a, chlorophyll b and nitrate reductase activity was recorded when MSE was applied with N fertilizer. Accordingly, using of Moringa extracted secondary metabolites to suppress AOB growth in the soil is a significant strategy to reduce nitrification rate and N loss from soils, and therefore increase NUE as well as reducing NO3- accumulation in potato tubers.

Hierarchical Graphene-Scaffolded Silicon/Graphite Composites as High Performance Anodes for Lithium-Ion Batteries.

To better couple with commercial cathodes, such as LiCoO2 and LiFePO4 , graphite-based composites containing a small proportion of silicon are recognized as promising anodes for practical application in lithium-ion batteries (LIBs). However, the prepared Si/C composite still suffers from either rapid capacity fading or the high cost up to now. Here, the facile preparation of hierarchical graphene-scaffolded silicon/graphite composite is reported. In this designed 3D structure, Si nanoparticles are homogeneously dispersed on commercial graphites and then uniformly encapsulated in the hierarchical graphene scaffold. This hierarchical structure is also well characterized by the synchrotron X-ray computed nanotomography technique. When evaluated as anodes for LIBs, the hierarchical composite, with the Si weight ratio of 5 wt%, exhibits a reversible capacity of 559 mA h g-1 at 75 mA g-1 , suggesting an unprecedented utilization of Si up to 95%. Even at 372 mA g-1 , the composite can still maintain a high capacity retention of 90% after 100 cycles. Coupled with the LiFePO4 cathode, the full cell shows the high capacity of 114 mA h g-1 at 170 mA g-1 . The excellent Li-storage properties can be ascribed to the unique designed hierarchical structure.

Counting-loss correction for X-ray spectra using the pulse-repairing method.

Facing the technical problem of pulse distortion caused by frequent resetting in the latest high-performance silicon drift detectors, which work under high-counting-rate conditions, a method has been used to remove false peaks in order to obtain a precise X-ray spectrum, the essence of which eliminates distorted pulses. Aiming at solving the problem of counting-loss generated by eliminating distorted pulses, this paper proposes an improved method of pulse repairing. A 238Pu source with activity of 10 mCi was used as the measurement object, and the energy spectrum obtained by the pulse repairing method was compared with that obtained by the pulse elimination method. The ten-measurement results show that the pulse repairing method can correct the counting-loss caused by the pulse elimination method and increase peak area, which is of great significance for obtaining a precise X-ray energy spectrum.

Counting-loss correction for X-ray spectroscopy using unit impulse pulse shaping.

High-precision measurement of X-ray spectra is affected by the statistical fluctuation of the X-ray beam under low-counting-rate conditions. It is also limited by counting loss resulting from the dead-time of the system and pile-up pulse effects, especially in a high-counting-rate environment. In this paper a detection system based on a FAST-SDD detector and a new kind of unit impulse pulse-shaping method is presented, for counting-loss correction in X-ray spectroscopy. The unit impulse pulse-shaping method is evolved by inverse deviation of the pulse from a reset-type preamplifier and a C-R shaper. It is applied to obtain the true incoming rate of the system based on a general fast-slow channel processing model. The pulses in the fast channel are shaped to unit impulse pulse shape which possesses small width and no undershoot. The counting rate in the fast channel is corrected by evaluating the dead-time of the fast channel before it is used to correct the counting loss in the slow channel.

Selection and identification of novel peptides specifically targeting human cervical cancer.

Cervical cancer is the second most commonly diagnosed cancer and the third leading cause of cancer deaths among females in underdeveloped countries. This study aimed to identify several novel cervical cancer-specific targeting peptides (CSPs) to provide new methods for the effective diagnosis and treatment of cervical cancer. Peptide library screening in vivo was performed on human cervical cancer xenografts with Ph.D.™-12 and C7C phage display peptide libraries. Two specific peptide sequences (GDALFSVPLEVY and KQNLAEG), which were enriched in tumors, were screened, and respectively, named CSP-GD and CSP-KQ through three rounds of biopanning. The in vivo tumor-targeting ability of these peptides was identified by injecting them into mice with cervical cancer xenograft. CSPs were compounded and labeled with fluorescein isothiocyanate (FITC). The specificity and affinity of FITC-CSPs were evaluated in human cervical cancer cell lines and tissue microarrays in vitro by immunofluorescent staining. Results showed that FITC-CSP-GD and FITC-CSP-KQ evidently and specifically bound to the cell membrane and cytoplasm of SiHa, ME-180, and C-33A cells in vitro. In human cervical cancer tissue, FITC-CSP-GD and FITC-CSP-KQ strongly targeted human cervical adenocarcinoma and cervical squamous cell carcinoma tissues, respectively. A bright FITC signal was located mainly on the cell membrane and cytoplasm of tumor cells. In conclusion, the novel 12-residue peptide CSP-GD and 7-residue peptide CSP-KQ could specifically target human cervical cancer and may have the potential to be used in the diagnosis and targeted therapy of cervical cancer.

[Study on the High Speed and Precision Gaussian Function Fitting Algorithm for Nuclear Single Spectral Peak].

In nuclear spectrum, Gaussian function least square fitting is a commonly used method. Usually the method has high precision, but it is very much sensitive to noise, which causes that the residual vector is larger near the peak in the Gaussian function. To solve the problem, Gaussian function least square fitting was deduced particularly, and the causes are analyzed. As a result, Gaussian function weighted least square fitting is proposed, i.e., a weight factor, which had an opposite tendency to the data weight reduction tendency after taking logarithm, or it had the same tendency to the origin data. This was introduced based on Gaussian function least square fitting to reduce noise sensitivity. In the process of solving Gaussian parameter, to improve the real-time performance, the solution process of inverse matrix was transferred to the solution process of simple equations because the computation of inverse matrix was time consuming. Gaussian function parameter, amplitude, center value and variance, were given with the fast calculation formulas. By applying these two methods to the practical fitting of 55Fe characteristic X-ray single spectrum peak, respectively, the results show that Gaussian function weighted least square fitting is more satisfactory. It indicates the proposed method can decrease the noise sensitivity and reduce the residual vector near the peak; in addition, the fitting precision is also improved. What's more, the real-time performance is improved by applying fast calculation formulas, which makes it possible to apply the proposed method to portable equipment efficiently.

Study on Heavy Metal Detection in Soil with Improved EDXRF.

Due to the low precision and accuracy of trace heavy metals detection wiith traditional energy dispersive X-ray fluorescence (EDXRF) system, an improved EDXRF system is proposed. In order to reduce the influence of reflected rays, the sample is irradiated with the incident X-rays vertically, and the detector is placed in parallel with the sample's section. The sample is connected with detector through collimator. With improved EDXRF measures certified reference materials, the results show that the detection limit of the improved EDXRF system for Mo，Zn，Cu，Pb，Zr，Nb is 0.4，6.68，1.97，6.84，1.60，7.59 mg·kg-1 respectively and the logarithm deviation of each element in the standard samples is between 0 and 0.05. The RSD%(GBW) is less than 7 as the element content is more than three times of the detection limit, and it is below 15 when the element content is less than three times of the detection limit. The soil samples collected from Da Xing'an Ling region are applied to verify the improved EDXRF system. The proposed EDXRF system can improve the measurement accuracy of trace heavy metal detection in soil, satisfying the requirements of geologic exploration.