Search

Objective To summarize the electrophysiological and muscle pathological characteristics of Lambert - Eaton myasthenic syndrome (LEMS). Methods and Results Twelve LEMS patients referred to China - Japan Friendship Hospital between January 2010 and December 2021 were included. Clinically, they all showed proximal muscle weakness and reduced or disappeared tendon reflexes. Electrophysiologically, all 12 patients showed decreased compound muscle action potential (CMAP) amplitudes, normal distal motor latency (DML), and normal motor and sensory conduction velocities. Ten patients underwent repetitive nerve stimulation (RNS) test: all had amplitude increments of more than 100% at high - frequency RNS, and 8 had amplitude decrements of more than 15% at low - frequency RNS. Three patients completed the post-exercise facilitation (PEF) test: the ulnar nerve CMAP amplitude reached a peak immediately after maximum voluntary contraction of the abductor digiti minimi for 5-10 s and then gradually decreased to near baseline level after contraction for 60 s; the ulnar nerve CMAP amplitude reached a peak immediately after maximum voluntary contraction for 10 s, and then rapidly decreased to near baseline level after 15 s. On needle EMG, 8 patients showed normal motor unit action potential (MUAP), 3 showed short - duration MUAP mimicking myopathy, and one showed long - duration MUAP mimicking neuropathy. Two patients with normal MUAP underwent biceps biopsy, which showed selective type Ⅱ fiber atrophy. Conclusions Electrophysiologically, CMAP amplitudes of LEMS patients are usually diffusely low or borderline. LEMS patients have amplitude increments of more than 100% at high-frequency RNS, and some have amplitude decrements of more than 15% at low-frequency RNS. PEF test shows a transient but significant CMAP amplitude increase after 5-10 s maximum voluntary contraction. Needle EMG is usually normal, but some show myogenic lesions, and some show neurogenic lesions. Muscle biopsy shows selective type Ⅱ fiber atrophy. Needle EMG myogenic lesion may not be associated with pathologically selective type Ⅱ fiber atrophy.

Currently, most research on recognizing unsafe behaviors of underground personnel focuses on improving precision through computer vision. However, underground areas are prone to occlusion, unstable lighting, and reflection, making it difficult to accurately recognize unsafe behaviors using computer vision technology alone. Especially, similar actions such as climbing ladders and holding ladders during climbing operations are easily confused during the recognition process, posing safety hazards. In order to solve the above problems, a multi-modal detection method for holding ladders in underground climbing operations is proposed. This method analyzes surveillance video data from two modalities: visual and audio. In terms of visual modality, the YOLOv8 model is used to detect the presence of ladder. If there is a ladder, the position coordinates of the ladder are obtained, and the video segment is put into the OpenPose algorithm for pose estimation to obtain the features of various skeletal joint points of the human body. These skeletal joint point sequences are then placed into improved spatial attention temporal graph convolutional networks(SAT-GCN) to obtain human action labels and their corresponding probabilities. In terms of audio modality, the PaddlePaddle automatic language recognition system is used to convert speech into text, and the bidirectional encoder representations from transformers (BERT) model is used to analyze and extract the features of text information, so as to obtain the text label and its corresponding probability. Finally, the information obtained from the visual and audio modalities is fused at the decision-making level to determine whether there is a dpersonnel holding ladders for underground climbing operations. The experimental results show that in action recognition based on skeleton data, the optimized SAT-GCN model improves the recognition precision of three types of actions: holding, climbing, and standing by 3.36%, 2.83%, and 10.71%, respectively. The multi-modal detection method has a higher recognition accuracy than the single modal method, reaching 98.29%.

Hydrogels prepared by hydroxypropyl starch have better tensile properties than ordinary starch, but their mechanical properties are relatively poor. In this paper, effect of the heat-moisture treatment on the physical, chemical and the gel properties of hydroxypropyl starch was studied. Compared with the control group, the thermal stability of starch has been improved and the maintenance value decreased from 12.55 J/g to 6.58 J/g. The XRD analysis showed that the crystallicity of the strength from 30.4% to 19.6%. The double helix in strength was first destroyed by heat-moisture treatment. The peak viscosity of hydroxypropyl starch first rose to about 5 000 cp and then dropped to about 3 000 cp. The TPA and the rheological analysis showed that the hardness of the starch increased after the heat treatment of 223.51 g to 463.50 g and the storage elastic module increased, indicating that wet heat treatment improved the mechanical properties of the starch.

BACKGROUND Lignin is widely distributed in vascular plants, and lignin-derived phenolic compounds generated by decomposition could provide information on the source of organic matter and the degradation degree of lignin. The conventional method for lignin deconstruction is complex and involves lignin hydrolysis via alkaline/acid chemical reagents. The analytical technique pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) breaks the chemical bonds of large molecule compounds by instantaneous high temperature to generate a series of small molecule compounds without introducing pretreatment methods such as chemical extractions, realizing the online analysis of complex organic matter that is not easy to be gasified. This technique is characterized by low sample volume, high organic matter extraction ratio, good reproducibility, and convenient operation. It has been shown that the high-temperature cracking products of peat and lake sediments are similar to the results of traditional CuO oxidative decomposition. The distribution characteristics of phenolic compounds indicate the vegetation type and organic matter degradation characteristics. However, the optimization of analytical methods, application of environmental indication significance, and comparative studies of different matrix samples are still needed. OBJECTIVES (1) Investigate suitable analytical methods for decomposing lignin in lake sediment samples and identify pyrolytic phenolic compounds in the sediments of Yiheshariwusu Lake in the northeast semi-arid region of China (Fig.E.1A, B). (2)Discuss the distribution characteristics of phenolic compounds in the sediments of Yiheshariwusu Lake. (3) Reveal the correlation between pyrolytic lignin phenols and regional climate change in the study area by combining traditional climate proxies, and provide an effective indicator for interpreting the response of terrestrial ecosystems to global climate change. METHODS (1) Analytical method: An optimized analytical method of Py-GC/MS was established and applied to evaluate lignin-derived phenolic compounds in typical arid lake sediment. Samples were heated to 650℃ for 20s (heating rate 20℃/ms) and pyrolysis products were injected into the gas chromatography (GC) system in split mode, then separated in a nonpolar, low-bleed fused silica column (DB-1MS, 60m, 0.25mm i.d., 0.25μm film thickness, J&W). The GC oven program was set to increase from 40 to 320℃ at a rate of 4℃/min, and left at 320℃ for 18min. With internal electron ionization and ion trapping, the compounds were fragmented and identified in full scan mode (40-450amu). Blank and duplicate samples were analysed for quality control.(2) Establishment of climatic proxy: Yiheshariwusu was selected as a typical arid lake and pyrolytical phenolic compounds of sediment cores were analysed. Historical variation of phenolic compound combing with radiocarbon dating results were revealed. According to "demethyl/demethoxy" oxidation reaction pathway of microorganisms to lignin, indicator related to degradation degree of lignin was established, and by comparing the indicators with conventional climate proxies previously published in the region, correlations between the indicators and climate features such as effective precipitation can be explored. RESULTS (1) Py-GC/MS analysis method for phenolic compounds was optimized. Phenolic compounds in the total pyrolytic products of sediments were categorized into 2 groups according to the type of functional group: alkyl-phenols (phenol compounds, PHs) and methoxy-phenols (lignin monomer compounds, LGs), which are further divided into o-, m- and p-compounds according to the position of the substituent on the benzene ring structure. Based on fine characterization of organic matter composition in the sediments of Yiheshariwusu Lake in Inner Mongolia, 21 phenolic compounds were identified and analyzed, including 9 PHs and 12 LGs (Table 1). Pyrolysis temperature is the main factor affecting the results of Py-GC/MS analysis of sediment organic matter fingerprinting. By discussing the effect of different pyrolysis temperatures on the distribution characteristics of the total pyrolytic products at 450℃, 550℃ and 650℃, it was determined that the relative concentration of lignin phenolic compounds increased significantly with increasing pyrolysis temperature. The ether bond (C—O—C) connecting the lignin skeleton structure benzene propane structural unit was further broken as the temperature was increased from 450℃ to 650℃. The relative concentration of phenolic compounds in the pyrolysis compounds reached the highest proportion (16.46%), while the proportion of aromatic hydrocarbons and aliphatic hydrocarbons increased by 3.98% and 10.26%, respectively. The natural macromolecules, which are not easily vaporized, are gradually cleaved into smaller ionic fragments of phenolic compounds under high pyrolysis temperature. As the cleavage temperature increases to 650℃, the flux of phenolic compounds into the chromatographic system increases and the gas chromatographic response is gradually enhanced, with the phenolic compounds reaching the highest ionic intensity response. At the same time, the unit peak area, shape and signal-to-noise ratio were all improved, which improved the accuracy of phenolic compound identification and analysis.(2) Distribution characteristics of phenolic compounds in Yiheshariwusu Lake were discussed. According to AMS 14C age data, historical variation of total phenolic compounds, PHs and LGs in lake sediment are generally consistent since 6.7ka, showing the characteristics of high relative concentration of 6.7-4.0ka and low concentration since 4.0ka. The variation characteristics of o-PHs, m-PHs, and p-PHs are consistent with total PHs, yet the change characteristics of p-LGs and LGs are different, the relative concentration of p-LGs decreased significantly near 5.4ka and remained at a low level since 3.8ka (average relative concentration of 0.29%). Combined with the lithological characteristics of sediment cores, relative concentration of total phenolic compounds and PHs decreased significantly around 4.0ka, probably due to the change of sedimentary lithology from sand to clay with smaller grain sizes during 4.0-3.8ka, where compounds with smaller molecular weights were preserved in the sediments, and the relative concentration of aliphatic hydrocarbons (e.g., n-alkanes, n-alkenes) and aromatic hydrocarbons significantly increased.(3) Environmental indication significance of phenolic compounds was studied. According to previous studies of free n-alkanes distribution proxies (e.g., ACL23-33), higher relative concentration in lake sediments of p-PHs indicated major herbaceous source of lignin, however, significant differences in the mean relative concentration of p-PHs and LGs indicated significant microbial degradation of organic matter. The mean value of p-PHs/p-LGs for Yiheshariwusu Lake sediments was 16.41 (n=31, range of 4.36-37.31), showing an overall increasing trend since 6.7ka, reflecting a gradual increase in microbial activities. p-PHs/p-LGs showed a consistent trend and negative correlation with δ13C27-33 (n=31, R=-0.77, p < 0.01), meanwhile, variation of p-PHs/p-LGs positively correlated with the trend of increasing pollen of Chenopodiaceae and Poaceae in Hulun Lake sediment (n=31, R=0.54, p < 0.01), and on a larger scale, p-PHs/p-LGs are consistent and positively correlated with the gradual increase in the standardized precipitation index since 6.7ka in the northern hemisphere mid-latitudes (n=31, R=0.62, p < 0.01) (Fig.E.1C). CONCLUSIONS The suitable pyrolysis temperature for Py-GC/MS analysis of phenolic compounds in the sediments of Yiheshariwusu Lake is 650℃. The value of degradation index p-PHs/p-LGs corresponds to the degree of lignin degradation, and the larger the value, the stronger the microbial degradation. Applying the p-PHs/p-LGs index to the sediment samples of Yiheshariwusu Lake, the result show that degradation index (p-PHs/p-LGs) and the carbon isotope of free n-alkanes δ13C27-33 has solid correlation since 6.7ka, indirectly indicating the change of effective precipitation, as the climate turned wet generally since 6.7ka, with terrestrial higher plants dominant, humid climate and sufficient organic matter provided a suitable living environment and relatively stable nutrient source for microorganisms, and the degradation generally increased. Since effective precipitation decreased during 6.3-5.5ka and 4.1-3.6ka, the degradation of lignin by microorganisms was relatively weakened. The p-PHs/p-LGs index corresponds to the characteristics of effective precipitation in the Hulun Buir region, revealing the correlation between microbial degradation and humidity change in arid and semi-arid regions. These findings provide a scientific basis for exploring the response of terrestrial ecosystems to climate change in the northern marginal region of the East Asian monsoon.

BACKGROUND The carbon isotope ratio of PAHs is stable in the migration and transformation, which is an important traceability index and can be analyzed by gas chromatography-isotope ratio mass spectrometry (GC-IRMS). For samples with low PAH content, meeting the detection limit of GC-IRMS is the premise for high-precision and accurate analysis of the carbon isotope ratio. OBJECTIVES To establish a PTV injection method with stronger intensity of PAHs, thereby improving the sensitivity of GC-IRMS carbon isotope analysis. METHODS Parameters of the programmed temperature vaporization (PTV) injector were optimized, including injection mode (constant temperature splitless, PTV splitless and solvent split), pressure process, sample transfer temperature and time, evaporation temperature and time, and splitless time. RESULTS The optimized parameters were PTV splitless, transfer temperature of 320℃, transfer time of 1.0min, injection pressure operating in a gradient of 40—60—70psi, evaporation temperature of 55℃, evaporation time of 2.5min, and splitless time of 1.5min. Pre-columns reduced the peak width and increased the peak intensity, especially high boiling point PAHs as benzo(a)pyrene, indeno(1, 2, 3-cd)pyrene, dibenzo(a, h)anthracene and benzo(g, h, i)perylene increased by 50%-100%. The precision of δ13C of 16 PAHs determined by the optimized PTV-GC-IRMS were within 0.5‰. The fractionation within the system can be corrected by two PAH references. CONCLUSIONS The optimized PTV-GC-IRMS can adjust the precision and accuracy of compound-specific carbon isotope analysis of PAHs at low concentrations, and expand the applicability of isotope tracing in environmental studies.

BACKGROUND Methylene chain backbone compounds (MCCs) in lake sediments are sensitive to climate change, and changes in environmental conditions could promote the transformation of MCCs lipids between free and bound states, hence providing a series of biomarkers for paleoclimate reconstruction. In previous studies, free MCCs lipids were typically extracted by mixed solvents, bound MCCs lipids with chemical bonding or physical adsorption could not be obtained by organic solvent extraction, and the indicator information of the characteristics of bound components on paleoclimate change was missing. OBJECTIVES To study the suitable analytical conditions for bound MCCs lipids, and establish proxy based on bound MCCs lipids to provide an effective tool for paleoclimate reconstruction of terrestrial ecosystems. METHODS Optimized analytical method of pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) was established and used to evaluate the bound MCCs in typical Desert Lake sediment. RESULTS Total of 71 bound MCCs compounds were identified and analyzed based on fine characterization of organic matter composition in the sediments of the Yiheshariwusu Lake in Inner Mongolia. Pyrolysis temperature was the main factor affecting the distribution characteristics of bound MCCs in sediment. Low pyrolysis energy under 450℃ led to insufficient resolution of bound MCCs. At 550℃ and 650℃, total bound n-alkanes, n-alkenes, and n-alkan-2-ones were on-line separated, identified and analyzed. The average chain length characteristics of bound n-alkanes at 550℃ and the carbon isotope of free n-alkanes as a traditional climate substitute index δ13C27-33 had the best correlation (R=0.83, n=11, p < 0.01). CONCLUSIONS Proxy ACL25-31 of bound n-alkanes respond to the change characteristics of regional effective precipitation, identify the drought periods around 5.6ka and 3.9ka in the region, reflect the intensity change of East Asian summer monsoon, and correspond to the change of effective precipitation in the mid-latitude of the northern hemisphere.

The major constituents of sand are silica and silicates. The facile and low-cost purification technology of silica from natural sand is of magnificent importance to the industrial applications of silicon-based materials. Herein, we report a green, low-cost, and universal method to purify silica from natural sand. Sand from deserts, rivers, and seas is selected as the representative of natural sand. The initial purity of silica is 52.1 wt% for desert sand, 39.3 wt% for river sand, and 35.8 wt% for sea sand. High-purity silica has been successfully separated and purified from natural sand via ball milling, reacting with 30 bar CO2 and hydrochloric acid. The purity of silica derived from natural sand reaches >96 wt%. In this work, the mechanism for the purification of silica from natural sand is discussed. This study provides a new method to separate high-purity silica from natural sand without the generation of toxic and harmful substances.

Objective To investigate the clinical characteristics of neuromyelitis optica spectrum disorders (NMOSDs) with other autoimmune diseases. Methods and Results Retrospective analysis was performed on 55 NMOSDs patients admitted to Peking University Third Hospital from June 2014 to January 2019. There were 10 NMOSDs patients with autoimmune diseases, including 5 patients with Sjögren's syndrome (SS), 2 patients with Hashimone's thyroiditis (HT), one patient with rheumatoid arthritis (RA), one patient with systemic lupus erythematosus (SLE), and one patient with undifferentiated connective tissue disease. The proportion of females with autoimmune disease (adjusted χ2=3.842, P=0.050) and positive of anti⁃AQP4 antibody (adjusted χ2=4.303, P=0.038) was higher than that of females without autoimmune diseases. Among 10 patients of NMOSDs with other autoimmune diseases, 9 patients involved spinal cord, 3 cases only involved cervical spinal, 2 cases only involved thoracic spinal, 4 cases involved both cervical and thoracic spinal at the same time, 4 cases involved optic nerve, one case involved only optic nerve. There was brain lesions in 2 cases, one case involved medulla oblongata. The imaging characteristics of spinal cord lesions were consistent with those of patients with NMOSDs. The length of the lesions were all longer than 3 vertebral bodies, and the longest lesions involved 10 segments. Conclusions NMOSDs is easy to be combined with other autoimmune diseases, which are more common in women, and the rate of positive of anti⁃AQP4 antibody is higher, which should be paid attention to.

BackgroundAutoimmune neutropenia (AIN) is a common chronic neutropenia in children, but it in children has been rarely reported.ObjectiveTo analyse clinical characteristics, diagnosis, treatment, and follow-up of children with AIN, aiming at providing support for clinicians.MethodsA retrospective design was used. Participants were 22 children with AIN recruited from Department of Pediatrics, Peking University First Hospital from 2012 to 2020. Their clinical and follow-up data were collected and analyzed.ResultsOf the 22 cases, 15 were male and 7 were female; with 6 months as the median initial diagnosis age. Among the results of 82 routine blood tests performed for all cases, severe, moderate and mild neutropenia accounted for 62.2% (51/82) , 30.5% (25/82) , and 7.3% (6/82) , respectively. Two cases (9.1%) were diagnosed with moderate neutropenia and other 20 (90.1%) were diagnosed with severe neutropenia by the lowest absolute neutrophil count (ANC) . Six children (27.3%) also had other clinical manifestations besides neutropenia. Twelve cases (54.5%) underwent the examination of bone marrow cell morphologies. Six cases (27.3%) underwent gene test. 95.5% of the cases had infections, and 54.5% of them had severe infections, but no life-threatening infections. The leading pathogen of infections was virus. The upper respiratory tract was the most common infected area. By the end of September 2021, the ANC of 11 cases returned to the normal level, and the median of AIN of them was 25 (range: 7-42) months.ConclusionMost AIN children had moderate to severe neutropenia, and they were prone to infections mostly caused by virus, and the most usually were upper respiratory tract infections, but rarely life-threatening. The median duration of AIN, a self-limited disease, for our reported cases was 25 months.

BackgroundShwachman-Diamond syndrome (SDS) is a rare autosomal recessive genetic disease that has complex and various clinical presentations. With the increase in application and clinical sensitivity of genome sequencing, the diagnoses of SDS in children and adults using genome sequencing have increased significantly, but most Chinese SDS patients have not received systematic and standardized treatment after diagnosis.ObjectiveTo analyze the clinical characteristics, diagnosis and treatment of three children with SDS, expecting to improve clinicians' recognition of this disease, reduce the possibilities of missed diagnosis and misdiagnosis, and standardize the treatment of diagnosed children.MethodsData of three children with SDS were collected from Department of Pediatrics, Peking University First Hospital from October 2018 to October 2020, including clinical manifestations, laboratory examination, gene analysis, treatment and follow-up, and were analyzed. In combination with the review of other relevant literature, the diagnosis and treatment of pediatric cases of SDS were summarized.ResultsAmong the three cases encountered and treated by us, two were female and one was male. All of them had recurrent infection, fatty diarrhea, short stature and malnutrition. Case 2 also had syndactyly. Auxiliary tests suggested that all these cases had neutropenia and abnormal liver function. Besides that, case 1 also had severe anemia, and case 2 had thrombocytopenia. Two compound heterozygous mutations of SBDS gene, that is, c.258 + 2T>C and c.184A>T, were found in all three cases. For treatment, all three patients were given pancreatic enzyme replacement therapy, nutritional support, and hepatoprotective treatment. The anemia of case 1, which was dependent on suspended red blood cell transfusion, was obviously improved after low-dose prednisone treatment.ConclusionSDS is a disease with multiple systems involved. Gene detection is helpful to the early diagnosis of SDS. Comprehensive, multidisciplinary treatment is needed. Hematopoietic stem cell transplantation with reduced dose pretreatment can improve some clinical manifestations, but the transplantation indications should be strictly controlled. Low dose and short course of glucocorticoid could be used to reduce the dependence on blood products for those with low erythropoiesis and no hematopoietic stem cell transplantation conditions.

BACKGROUND Tracing the source of polycyclic aromatic hydrocarbons (PAHs) by the compound-specific carbon isotope is becoming increasingly popular. For precise carbon isotope analysis, a pretreatment process is required to reduce co-outflow and unresolved complex mixture (UCM). Some existing studies require more instrumentation, such as high-performance liquid chromatography (HPLC). In addition, little attention has been paid to PAHs with a ring number less than 3. OBJECTIVES To establish a good separation method of 16 PAHs for meeting the requirements of compound-specific carbon isotope analysis. METHODS The effects of solid phase extraction (SPE) cartridges with amino and silica fillers were compared, and 10 eluent solvents were used on the separation, purification and enrichment effects of PAHs. Gas chromatography (GC) was used to test the separation and purification effect, and gas chromatography-isotope ratio mass spectrometry (GC-IRMS) was used to analyze compound-specific carbon isotopes. RESULTS More than 20% of the naphthalene and acenaphthene in the amino cartridge cannot be completely separated from the alkanes and unresolved peaks. The silica gel SPE cartridge has better impurity removal and separation effects than the amino cartridge. Choosing 1000mg/6mL silica gel SPE cartridge, using 6mL n-pentane to elute UCM and alkanes, and 5mL n-pentane-dichloromethane (70:30, V/V) to elute PAHs, and GC to conduct a preliminary inspection of the separation and purification effect, and GC-IRMS for individual carbon isotope analysis. The recovery of 16 kinds of PAHs was 79%-128%, the relative standard deviation was 2%-13% (1σ, n=6), and the analysis accuracy of the single carbon isotope ratio (δ13C) was 0.1‰-0.75‰. CONCLUSIONS The method greatly reduces the interferences of co-outflow and UCM to compound-specific carbon isotope analysis of PAHs, especially the low cyclic PAHs. No significant carbon isotope fractionation of PAHs is observed during purification, which satisfies compound-specific carbon isotope analysis requirements.

BACKGROUND Before analyzing the carbon isotopes of n-alkanes by gas chromatography-gas isotope mass spectrometry (GC-IRMS), it is necessary to pre-separate and enrich n-alkanes and isoparaffins in saturated hydrocarbon samples. Whether the carbon isotope fractionation of n-alkanes occurs is the key for the high-precision analysis of the carbon isotope ratio. OBJECTIVES To determine isotopic fractionation characteristics for n-alkanes during column chromatography and molecular sieve separation. METHODS Saturated hydrocarbon components were extracted with a 500mg/3mL SPE silica gel column using 2mL n-pentane. After separating by a 5Å molecular sieve and extracting by a mixture solvent of cyclohexane and n-pentane, n-alkanes were concentrated and analyzed by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). RESULTS During column chromatographic separation, the carbon isotope ratio of most n-alkanes differed from -0.2‰ to 0.2‰. When n-alkanes was not completely complexed by 5Å molecular sieve, the uncomplexed alkane carbon isotope was about 0.7‰ heavier, and weak carbon isotope fractionation occured, but it did not affect the eluted n-alkanes carbon isotope ratio. Eluted with cyclohexane-n-pentane mixed solvent, the carbon isotope values before and after the elution differed from-0.2‰ to 0.5‰, and eluted in the same way for the second time, the difference between the eluted n-alkanes carbon isotope and simulate sample was between -0.3‰ and 0.2‰. Analyzing the carbon isotope ratios of n-alkanes with different recoveries (>20%), the difference between carbon isotopes of n-alkanes before and after pretreatment was within 0.3‰. It was found that when the recovery was as low as 20%, the carbon isotope ratios did not undergo significant fractionation. CONCLUSIONS The column chromatography-5Å molecular sieve adsorption and mixed solvent elution method is suitable for the analysis of carbon isotope ratios of normal alkanes, which yields a recovery greater than 20%.

BACKGROUND Seawater cultured gray Akoya pearls have become popular as jewelry in the recent years. In the early stage, some research focused mainly on investigating the cultured environment of seawater or freshwater pearls, element occurrence characteristics of each structural unit, irradiation treatment and the identification method of irradiated pearls. OBJECTIVES To further study the gemological characteristics and fine microstructure of a type of gray pearl with a white nucleus. METHODS Ultraviolet-visible reflection spectrum, micro-infrared spectrum and scanning electron microscope methods were used. RESULTS A brown transition layer of organic matter between the nacre and nucleus was discovered, which measures several microns in thickness. A layer with no fixed morphology composed of calcite and vaterite in the nacre near the brown transition layer was also discovered. Quasi plates of aragonite exist in the nacre near the surface of the pearl. The morphology of these aragonite tablets in the middle area of the nacre was more regular, the thickness of individual aragonite plate gradually decreased in the direction from the nucleus to the surface of the pearls. The reflectance spectrum of the entire pearl surface was consistent with the spectral characteristics of the outer single nacre. The brown transition layer had no direct effect on the UV-Vis reflectance spectrum of the entire pearl. Therefore, whether or not the brown transition layer affected the gray appearance of the pearl needs further discussion. CONCLUSIONS The research work has important guiding significance for the coloring mechanism of gray Akoya pearls and the identification of the formation attributes. It can also aid in the recognition of the fine structure and mineralization characteristics of pearls with a thin layer of nacre of 0.3mm to 0.6mm.

BACKGROUND Heavy metal elements in sediment can migrate in an active state under natural action, which has potential bioavailability and potential regional ecological risks. The use of near-infrared spectroscopy (NIRS) technology to study the response mechanism of samples of different matrices can provide a non-destructive and rapid analysis method for evaluating the active state of heavy metals and provide a basis for ecological risk research. OBJECTIVES To reveal the characteristics of active metal elements in lagoonal wetland sediment and evaluate their ecological risk. METHODS Sediment core and soil samples near by the drilling site were analyzed using both spectral and chemical method. NIR spectra of dry-freezed sample were collected by infrared spectrometer with integrating sphere. Based on the near infrared spectroscopy analysis technique, near infrared spectrum were collected by the integrating device within range of 4000-10000cm-1 (1000-2500nm), at the resolution of 2cm-1. Meanwhile the chemical mobile fractions of heavy metal elements were extracted from soil and sediment samples by diluted nitric acid, the dissolved concentrations of Co, Ni, Cu, Zn, Cd, Pb were determined by inductively coupled plasma-mass spectrometry (ICP-MS). With both chemical and spectral predicted value, the partial least squares regression prediction model had been developed and applied to determine mobile fraction of Co, Ni, Cu, Zn, Cd and Pb. RESULTS Area of absorption peaks at 7290-6390cm-1 and 4683-4000cm-1 related to O-H strentching along with AlAl-OH and Al(Mg)-OH bending indirectly indicate the active content of heavy metals. Spectral prediction results show that the changes in the active components of Co, Ni, Cu, Zn, Cd and Pb in the sediments of the Qilihai in the past 100 years corresponded to the three obvious changes from 1934 to 1948, 1956 to 1963, and 1976 to the present. The temperature increase also corresponded to large-scale human disturbances such as the construction of the Qilihai Reservoir in 1980. CONCLUSIONS The total and mobile fractions of Co, Ni, Cu, Zn, Cd and Pb in Qilihai sediments were lower than the ecological risk threshold specified in the national standard. The ecological risk of heavy metals released from wetlands towards nearby villages and farmland in the Qilihai catchment area was extremely low.

The effect of temperature (T) on stability of squeezed soybean oil (SSO) were studied by four characterization parameters (CPs, conductivity, peroxide value, isovolumetric combustion heat and acid value)similarities and differences of CPs characterization results were further compared.Under the fixed conditions of relative humidity was 40%, partial pressure of oxygen was 21 kPa, illumination was 800 lx and initial headspace rate was 50%, regulated and controled T to 30 ℃, 40 ℃, 50 ℃, 60 ℃ and 70 ℃ respectively,SSO test samples were oxidized continuously in airtight container for a long time, four CPs at different oxidation time (t) were multiple measured in the same time, curve of CP～t was plotted, kinetic equation was regressed, rate constant (k) and apparent activation energy were calculated, the prediction model of metamorphic time was established and coincidence rate was verified.The results show that CP changed significantly with the increase of T and the extension of t, the oxidative rancidity of SSO has characteristic of simple series reaction,the prediction model of metamorphic time has a good coincidence, CP was different, and there was a big difference in k.The stability of squeezed soybean oil of SSO should be described by multiple CPs.

The super maneuverability of aircraft is a key factor determining its success or defeat in air combat. The analysis and control of aircraft post stall maneuvering at a high angle of attack can greatly improve the aircraft maneuverability. When the aircraft performs a high-angle-of-attack maneuver, the aircraft's attack angle far exceeds the stall angle; thus, the aerodynamic and aerodynamic moment characteristics are not only strongly nonlinear but also have delay effects and strong coupling characteristics. Moreover, the linear control method based on the linearization of small disturbance hardly satisfies the control requirement because there is no typical leveling state. Traditional nonlinear control methods include nonlinear dynamic inverse, sliding mode control, and robust control for high-angle-of-attack maneuvering of aircraft. However, these methods rely on the accurate model of the aircraft and are greatly affected by modeling errors. To realize the high-angle-of-attack maneuver control for an aircraft with thrust vector, a three-channel decoupling control strategy based on active disturbance rejection control was proposed herein. Based on the public data of the third-generation fighter F16, a thrust vector model was developed. The desired triaxial moments were generated by the thrust vector nozzle combination. Active disturbance rejection controllers were independently designed in longitudinal, lateral, and heading channels. The unmodeled dynamics, uncertainty, and strong coupling between the channels were regarded as total disturbance, which was estimated and compensated online. The angular rate damping feedback term made the closed-loop dynamics of the original aircraft approximate a generalized object, which reduced the design order of the active disturbance rejection controller. As two typical post-stall maneuvers, Cobra maneuver and Herbst maneuver were selected for control strategy verification. The numerical simulation results show that the designed three-channel independent active disturbance rejection controllers can eliminate the strong coupling among channels and realize a high-angle-of attack maneuver for the aircraft with thrust vector. The Monte Carlo simulation results show that the control strategy has good robustness.

Avian pathogenicEscherichia coli (APEC) causes serious colibacillosis and significant economic losses. Data on profiles of virulence factors and antibiotic resistances among APEC strains are crucial to the control of infection. In this study, strains were isolated from eastern China, and the prevalence of virulence factors and distribution of antibiotic resistance were determined.

The authentication protocols are implemented to provide identity authentication for communication entities. With the increasing demand of network security and the development of technology, the anonymous authentication protocol for LBS (location based service) has gradually become a research hotspot and attracted extensive attentions, which provides anonymity of the user, confidentiality of location information and identity authentication simultaneously. An efficient and secure anonymous authentication protocol with enhanced privacy for location based service using asymmetric cryptography was proposed by Memon et al. in 2015. However, some scholars pointed out some weaknesses of Memon et al.'s protocol, such as the lack of resistance to password change attack, privileged insider attack and offline password guessing attack. They also pointed out the protocol failed to prevent adversaries from getting the session-specific temporary information. Besides, the mutual authentication was not perfect. Therefore, in this paper, we further analyze the security of Memon et al.'s protocol and propose an improved anonymous authentication protocol for location based service. We use the timestamp mechanism and rely on CDH (Computational Diffie-Hellman) problem to improve security primarily. The security of the proposed protocol is verified using BAN logic and the performance comparison and efficiency analysis are carried out. The results show that our improved protocol has higher security with little more computation cost.

Anthropogenic activities have substantially enhanced the loadings of reactive nitrogen (Nr) in the Earth system since pre-industrial times1,2, contributing to widespread eutrophication and air pollution3-6. Increased Nr can also influence global climate through a variety of effects on atmospheric and land processes but the cumulative net climate effect is yet to be unravelled. Here we show that anthropogenic Nr causes a net negative direct radiative forcing of -0.34 [-0.20, -0.50] W m-2 in the year 2019 relative to the year 1850. This net cooling effect is the result of increased aerosol loading, reduced methane lifetime and increased terrestrial carbon sequestration associated with increases in anthropogenic Nr, which are not offset by the warming effects of enhanced atmospheric nitrous oxide and ozone. Future predictions using three representative scenarios show that this cooling effect may be weakened primarily as a result of reduced aerosol loading and increased lifetime of methane, whereas in particular N2O-induced warming will probably continue to increase under all scenarios. Our results indicate that future reductions in anthropogenic Nr to achieve environmental protection goals need to be accompanied by enhanced efforts to reduce anthropogenic greenhouse gas emissions to achieve climate change mitigation in line with the Paris Agreement.

Nitrous oxide (N2O) is a greenhouse gas and stratospheric ozone-depleting substance with large and growing anthropogenic emissions. Previous studies identified the influx of N2O-depleted air from the stratosphere to partly cause the seasonality in tropospheric N2O (aN2O), but other contributions remain unclear. Here, we combine surface fluxes from eight land and four ocean models from phase 2 of the Nitrogen/N2O Model Intercomparison Project with tropospheric transport modeling to simulate aN2O at eight remote air sampling sites for modern and pre-industrial periods. Models show general agreement on the seasonal phasing of zonal-average N2O fluxes for most sites, but seasonal peak-to-peak amplitudes differ several-fold across models. The modeled seasonal amplitude of surface aN2O ranges from 0.25 to 0.80 ppb (interquartile ranges 21%–52% of median) for land, 0.14–0.25 ppb (17%–68%) for ocean, and 0.28–0.77 ppb (23%–52%) for combined flux contributions. The observed seasonal amplitude ranges from 0.34 to 1.08 ppb for these sites. The stratospheric contributions to aN2O, inferred by the difference between the surface-troposphere model and observations, show 16%–126% larger amplitudes and minima delayed by ∼1 month compared to Northern Hemisphere site observations. Land fluxes and their seasonal amplitude have increased since the pre-industrial era and are projected to grow further under anthropogenic activities. Our results demonstrate the increasing importance of land fluxes for aN2O seasonality. Considering the large model spread, in situ aN2O observations and atmospheric transport-chemistry models will provide opportunities for constraining terrestrial and oceanic biosphere models, critical for projecting carbon-nitrogen cycles under ongoing global warming.