Field test of high-power microwave-assisted mechanical excavation for deep hard iron ore

Microwave-assisted mechanical excavation has great application prospects in mines and tunnels,but there are few field experiments on microwave-assisted rock breaking.This paper takes the Sishanling iron mine as the research object and adopts the self-developed high-power microwave-induced fracturing test system for hard rock to conduct field experiments of microwave-induced fracturing of iron ore.The heating and reflection evolution characteristics of ore under different microwave parameters(antenna type,power,and working distance)were studied,and the optimal microwave parameters were obtained.Subsequently,the ore was irradiated with the optimal microwave parameters,and the cracking effect of the ore under the action of the high-power open microwave was analyzed.The results show that the reflection coefficient(standing wave ratio)can be rapidly(<5 s)and automatically adjusted below the preset threshold value(1.6)as microwave irradiation is performed.When using a right-angle horn antenna with a working distance of 5 cm,the effect of automatic reflection adjustment reaches the best among other antenna types and working distances.When the working distance is the same,the average temperature of the irradiation surface and the area of the high-temperature area under the action of the two antennas(right-angled and equal-angled horn antenna)are basically the same and decrease with the increase of working distance.The optimal microwave parameters are:a right-angle horn antenna with a working distance of 5 cm.Subsequently,in further experiments,the optimal parameters were used to irradiate for 20 s and 40 s at a microwave power of 60 kW,respectively.The surface damage extended 38 cm×30 cm and 53 cm×30 cm,respectively,and the damage extended to a depth of about 50 cm.The drilling speed was increased by 56.2%and 66.5%,respectively,compared to the case when microwaves were not used.

Study on the Installation and Construction Technology of the Transfer Stairway on the Track Platform on Bridge——Taking the Construction of the Jialing River Bridge in Zengjiayan of Chongqing City as an Example

The bridge deck on the Yuzhong side of Zengjiayan Jialing River Bridge is close to subway lines and light rail stations.It is necessary to set up transfer stairways on both sides of the bridge.The construction technology of installing and replacing with tunnel under special conditions is discussed to provide reference for bridge construction.

An open-end high-power microwave-induced fracturing system for hard rock

Microwave pre-treatment is considered as a promising technique for alleviating cutter wear. This paper introduces a high-power microwave-induced fracturing system for hard rock. The test system consists of a high-power microwave subsystem (100 kW), a true triaxial testing machine, a dynamic monitoring subsystem, and an electromagnetic shielding subsystem. It can realize rapid microwave-induced fracturing, intelligent tuning of impedance, dynamic feedback under strong microwave fields, and active control of microwave parameters by addressing the following issues: the instability and insecurity of the system, the discharge breakdown between coaxial lines during high-power microwave output, and a lack of feedback of rock-microwave response. In this study, microwave-induced surface and borehole fracturing tests under true triaxial stress were carried out. Experimental comparisons imply that high-power microwave irradiation can reduce the fracturing time of hard rock and that the fracture range (160 mm) of a 915-MHz microwave source is about three times that of 2.45 GHz. After microwave-induced borehole fracturing, many tensile cracks occur on the rock surface and in the borehole: the maximum reduction of the P-wave velocity is 12.8%. The test results show that a high-power microwave source of 915 MHz is more conducive to assisting mechanical rock breaking and destressing. The system can promote the development of microwave-assisted rock breaking equipment.

A novel true triaxial test system for microwave-induced fracturing of hard rocks

This study introduces a test system for microwave-induced fracturing of hard rocks under true triaxial stress.The test system comprises a true triaxial stress loading system,an open-ended microwaveinduced fracturing system,a data acquisition system,an acoustic emission(AE)monitoring system,and an auxiliary specimen loading system.Microwave-induced surface and borehole fracturing tests under true triaxial stress were fulfilled for the first time,which overcomes the problem of microwave leakage in the coupling loading of true triaxial stress and microwave.By developing the dynamic monitoring system,the thermal response and fracture evolution were obtained during microwave irradiation.The monitoring system includes the infrared thermometry technique for monitoring rock surface temperature,the distributed optic fiber sensing technique for monitoring temperature in borehole in rock,the AE technique and two-dimensional digital speckle correlation technique for monitoring the evolution of thermal damage and the rock fracturing process.To validate the advantages of the test system and investigate the characteristics of microwave-induced fracturing of hard rocks,the study demonstrates the experimental methods and results for microwave-induced surface and borehole fracturing under true triaxial stress.The results show that thermal cracking presented intermittent characteristics(calm eactiveecalm)during microwave-induced surface and borehole fracturing of basalt.In addition,true triaxial stress can inhibit the development and distribution of thermal cracks during microwave-induced surface fracturing.When microwave-induced borehole fracturing occurs,it promotes the distribution of thermal cracks in rock,but inhibits the width of cracks.The results also prove the reliability of the test system.

Microwave response characteristics and influencing factors of ores based on dielectric properties of synthetic samples

In order to understand the influence of different factors on the microwave response characteristics of ores,the effects of electrical conductivity,metal mineral content,compactness,metal mineral distribution,microwave frequency and temperature on the dielectric properties of synthetic ores(metal mineral and quartz)were studied.Microwave heating tests were carried out on three types of natural ores(Hongtoushan copper ore,Sishanling iron ore and Dandong gold ore)with significant differences in metal mineral contents.The test results showed that under microwave irradiation,the stronger the electrical conductivity of the metal minerals,the smaller the penetration depth in synthetic ore.For those metal minerals with lower electrical conductivity,the microwave absorption coefficient of the synthetic samples increases with increasing metal mineral content.For those metal minerals with higher electrical conductivity,the microwave absorption coefficient of the samples first increases and then decreases as the metal mineral content increases.When the metal minerals are distributed in layers,the penetration depth is much less than that given a uniform distribution.The penetration depth in the sample at microwave frequency of 915 MHz is greater than that at 2.45 GHz.The higher the electrical conductivity of metal minerals used in synthetic ores,the higher the high-temperature sensitivity of electromagnetic shielding coefficient(0.C-500.C).The Hongtoushan copper ore with high metal mineral content exhibits obvious size effect.The effects of ore structure and crystal particle size on the distribution characteristics of microcracks were discussed.Based on the test results,a quantitative prediction model of microwave sensitivity of ore was proposed,which provides guidance for the prediction of ore heating effect and the selection of microwave heating sequence of ore.

Vascular dementia has the highest hospitalisation rate in China:a nationwide hospital information system study

Background Although vascular dementia(VaD)is not uncommon in the hospital,most studies on VaD are community based.This study on VaD is the first to use a national hospital information system(HIS)in China.Methods This study was a hospital population-based cohort study,and data were acquired from the Hospital Quality Monitoring System,a Chinese national database that covers 1531 tertiary hospitals in China.The medical records in the HIS included demographic information,diagnoses,procedures,expenses,etc.VaD was diagnosed by hospital attending physicians and identified by the International Classification of Diseases(ICD)10 code(F01.0-F01.9).Results 1259(82.23%)tertiary hospitals were included in this study,and 274230 hospitalisation records of 123700 VaD patients from 2016 to 2018 were identified for analysis.VaD(51.27%)was the most common type of dementia in hospitalised patients.The age-adjusted and sex-adjusted hospital incidence of VaD was estimated to be 2.97 per 100000 person-years(95%CI 2.92 to 3.02).The mean age of VaD patients admitted to hospitals was 74.13±10.88,with more male(61.0%)patients.The main comorbidities were hypertension(67.2%),heart disease(63.6%)and cerebral infarction(55.5%).The mortality rate of VaD in hospital was 28.91‰(95%CI 28.0 to 29.9)between 2016 and 2018.The top 1 cause of death due to VaD was pneumonia and other respiratory disorders.Conclusions VaD is the most common form of dementia in hospitalised patients.It casts huge burdens on affected patients and their caregivers.Vascular risk factors are prevalent in VaD patients.Reducing these factors is essential to improve patient care.The leading causes of death by VaD are pneumonia and other respiratory disorders.Hospital care and the management of respiratory illness are critical for VaD care in the hospital.

Allergen immunotherapy in patients with atopic dermatitis allergic to house dust mite:A systematic review and meta-analysis

To the Editor:Atopic dermatitis(AD)is the most common chronic allergic skin disease worldwide.House dust mite(HDM)is the most prevalent aeroallergen and pathogenic cause,which triggers skin barrier disruption and polysensitization.Allergen immunotherapy(AIT)may be the only etiologic treatment to improve the natural history of AD by applying a dose of specific allergens to stimulate adaptive immunity in the body.[1,2]However,the effects of HDM AIT showed controversial results recently.This study aimed to investigate the effectiveness and safety of AIT for HDM.

Baseline Characteristics and Treatment Patterns of the Patients Recruited to the China Registry of Hepatitis B

Background and Aims: Chronic hepatitis B virus(HBV)in-fection remains a major public health problem globally.Here,we describe the baseline characteristics and treatment pro-files of HBV-infected patients recruited to the China Registry of Hepatitis B.Methods: Inclusion criteria were patients with different stages of chronic HBV infection and complete key data.Exclusion criteria were patients with hepatocellular car-cinoma.The baseline clinical,laboratory and treatment pro-files were analyzed.Results: Finally,40,431 patients were included.The median age was 43 years,with 65.2%being men and 51.3%being positive for hepatitis B e antigen(HBeAg).The most common initial diagnosis was chronic hep-atitis B(81.0%),followed by cirrhosis(9.3%),inactive carrier of hepatitis B surface antigen(HBsAg)(6.7%),and immune tolerant phase of hepatitis B infection(3.0%).Among the 21,228 patients who were on treatment,88.0%,10.0%and 2.0%received nucleos(t)ide analogues(NAs),interferon or combination of NAs and interferon,respectively.The propor-tion of patients who received preferred NAs(entecavir or te-nofovir disoproxil fumarate)had increased from 13.5%in 2003 to 79.7%in 2016.Conclusions: We concluded that middle-aged men accounted for most of the patients with chronic hepatitis B in this cross-sectional study.About half of the patients were HBeAg-positive.NAs were the most com-monly used therapy,and use of the preferred NAs had steadily increased in the past decade.

PolyvasculaR Evaluation for Cognitive Impairment and vaScular Events (PRECISE)-a population-based prospective cohort study: rationale, design and baseline participant characteristics

Background and purpose Cardiovascular diseases and dementia are two major diseases in the elderly.Atherosclerosis is associated with future vascular events and cognitive impairment.The PolyvasculaR Evaluation for Cognitive Impairment and vaScular Events(PRECISE)study is a population-based prospective cohort study with comprehensive evaluation of multiterritorial artery stenosis and plaque using advanced vascular imaging techniques and prospective collection of vascular events and cognitive assessments.Methods Between May 2017 and September 2019,the PRECISE study enrolled 3067 community-dwelling adults with ages between 50 and 75 years cluster sampled from six villages and four communities of Lishui city in China.Data are collected in face-to face interviews at baseline,2-year and 4-year follow-up visits.Brain MRI including high-resolution sequences for intracranial and carotidal arteries and CT angiography for thoracoabdominal arteries were performed at baseline and will be rescanned after 4 years.Cardiovascular/cerebrovascular events and cognitive assessment will be prospectively collected after the enrollment.Blood and urine samples were collected and biomarkers were tested at baseline.Results A total of 3067 subjects were enrolled,among which 53.5%were female with an average age of 61.2±6.7 years.Among them,2.8%,8.1%,43.1%and 21.6%had a history of stroke,coronary heart diseases,hypertension and diabetes mellitus,respectively.Conclusions The PRECISE study is a population-based prospective cohort study with comprehensive evaluation of atherosclerotic stenosis and plaque using advanced vascular imaging techniques.Data from this cohort provide us an opportunity to precisely evaluate polyvascular atherosclerosis and its association with future vascular events and cognitive impairment.

阿尔茨海默病的血液生物标志物:一项基于中国多中心的横断面和纵向研究

阿尔茨海默病(AD)的生物标志物在血液中含量可能因种族、老年性疾病与各种环境风险因素等不同而存在差异,尚缺乏系统性的研究来评估AD生物标志物在中国老年及AD患者人群中的变化以及是否具有准确预测脑内淀粉样蛋白沉积的能力.本工作为一项多中心纵向队列研究,共纳入来自全国各地6个不同临床中心的817个血液样本.研究测量了多个国际上通用的AD生物标志物,包括β-淀粉样蛋白40与42、磷酸化Tau(pTau)蛋白、总Tau蛋白、神经纤维丝轻链(NFL)和胶质纤维酸性蛋白(GFAP),并使用淀粉样斑块PET示踪剂和核磁结构影像对受试者进行综合评估.研究发现,APOE基因型与血浆pTau或血清GFAP组合的预测模型对脑内淀粉样斑块的沉积状态具有较好的区分能力.此外,研究还发现GFAP基线水平越高的患者其神经退行性变的速度越快.本研究结果基于多中心数据,论证了AD血液生物标志物在中国汉族人群中的实用性和应用前景,提示了血液pTau和GFAP是检测AD早期症状的有效指标,为我国AD的早期诊断和治疗提供了参考.

Photochemically induced thalamus infarction impairs cognition in a mouse model

Background Small subcortical infarcts account for up to 25%of ischaemic strokes.Thalamus is one of the subcortical structures that commonly manifest with lacunar infarcts on MRI of the brain.Studies have shown that thalamus infarction is associated with cognitive decline.However,due to the lack of proper animal models,little is known about the mechanism.We aimed to establish a focal thalamus infarction model,characterise the infarct lesion and assess functional effects.Methods Male C57BL/6J mice were anaesthetised,and Rose Bengal dye was injected through the tail vein.The right thalamus was illuminated with green laser light by stereotactic implantation of optic fibre.Characteristics of the infarct and lesion evolution were evaluated by histological analysis and 7T MRI at various times.The cognitive and neurological functions were assessed by behavioural tests.Retrograde tracing was performed to analyse neural connections.Results An ischaemic lesion with small vessel occlusion was observed in the thalamus.It became a small circumscribed infarct with reactive astrocytes accumulated in the infarct periphery on day 21.The mice with thalamic infarction demonstrated impaired learning and memory without significant neurological deficits.Retrogradely labelled neurons in the retrosplenial granular cortex were reduced.Conclusion This study established a mouse model of thalamic lacunar infarction that exhibits cognitive impairment.Neural connection dysfunctions may play a potential role in post-stroke cognitive impairment.This model helps to clarify the pathophysiology of post-stroke cognitive impairment and to develop potential therapies.

Evolution of chemical composition of fogwater in winter in Chengdu, China

Two sampling sites representing the urban and suburban area of Chengdu, China were sampled and analyzed for selected chemicals to characterize the evolution of the chemical composition of fogwater. A trend of total organic carbon （TOC） 〉 total nitrogen （TN） 〉 total inorganic carbon （TIC） was observed for both sites. Variation of inorganic ions indicated that inorganic pollutants were not accumulated in the fog. Concentrations of n-alkanes （C11-C37） at the urban site ranged from 7.58 to 27.75 ng/mL while at the suburban site concentrations were 2.57-21.55 ng/mL. The highest concentration of n-alkanes was observed in the mature period of fog （393.12 ng/mL） which was more than ten times that in the fog formation period （27.83 ng/mL） and the fog dissipation period （14.87 ng/mL）. Concentrations of Σ15PAHs were in the range of 7.27-38.52 ng/mL at the urban site and 2.59-22.69 ng/mL at the suburban site. Contents of PAHs in the mature period of fog （27.15 ng/mL） 〉 fog dissipation period （11.59 ng/mL） 〉 fog formation period （6.42 ng/mL）. Concentrations of dicarboxylic acids （C5-C9） ranged from 10.92 to 40.78 ng/mL, with glutaric acid （C5） as the dominant dicarboxylic acid. These data provide strong indications of the accumulation of certain organic chemicals of environmental concern in fog and fog water, and provide additional insights about processes in urban and suburban air acting on organic chemicals with similar physical chemical properties.