Overview of radar detection methods for low altitude targets in marine environments

In this paper,a comprehensive overview of radar detection methods for low-altitude targets in maritime environments is presented,focusing on the challenges posed by sea clutter and multipath scattering.The performance of the radar detection methods under sea clutter,multipath,and combined conditions is categorized and summarized,and future research directions are outlined to enhance radar detection performance for low-altitude targets in maritime environments.

Study on Skin Care Efficacy of the Active Ingredients in Camellia Japonica Flowers at High and Low Altitudes

The active ingredients of Camellia japonica flowers(CJF)at high and low altitudes,as well as their skin care efficacy were compared.The dried red CJF at high and low altitudes were ultrasonically extracted with 70%ethanol,and these extracts were concentrated and then diluted to a constant volume.The content of total flavonoids,total polyphenols and total proteins was tested and analyzed.In addition,DPPH free radical scavenging,inhibition of the formation of advanced glycation end products,and inhibitory activity against elastase was measured to compare their skin care efficacy in anti-oxidation,anti-glycation,anti-wrinkling and firming.The results showed that,based on the dry weight of CJF,the content of total flavonoids and total proteins of the CJF at high altitude was approximately 1.5 times of the CJF at low altitude,while the content of total polyphenols was approximately 2.4 times that of the CJF at low altitude.The skin care efficacy of CJF at high altitude was significantly better than that of the CJF at low altitude.This work could provide theoretical basis for the selection and application of Camellia japonica flowers in the field of cosmetics.

UP,UPAND AWAY! Innovation drives a new horizon in the low-altitude economy

Defined as activities inairspacebelow 1,000 meters,lowaltitude economy leverages manned and unmanned aircraft,driving integrated developmentacross industries.Whereas Western nations did get a head start in this sector,with the global push for the low-altitude economy beginning in 2016 as the United States Federal Aviation Administration issued Rule 107-governing the operation of commercial drones.

China Seeks to Grab Opportunities Brought about by the Low-Altitude Economy

Since the inclusion of the low-altitude economy in the government work report during the National People’s Congress and the Chinese People’s Political Consultative Conference in March,many cities have sought to enter this area first to seize the benefits of the low-altitude economy.According to incomplete statistics,17 provinces(municipalities,autonomous regions)in China have currently written the low-altitude economy into their 2024 government work report.In addition,cities such as Shenzhen,Guangzhou,Chengdu,Suzhou,Zhuhai,and Ganzhou have also included the low-altitude economy in their government work reports.More than 20 provincial and municipal governments,represented by Shenzhen,Hefei,Guangzhou and Chengdu,have introduced also policies to support the development of the low-altitude economy and its business ecosystem.

AIRCRAFT FLIGHT SAFETY ANALYSIS IN LOW ALTITUDE AIRSPACE

The low altitude airspace will be open in China, general aviation flights are tremendously increased. Whether aircrafts can fly safely and how to determine the requirements of safety flight are the problems needed to be confirmed. Under this circumstances, based on the international Civil Aviation Organization（ICAO） criteria and the standards made by CAAC, this paper adopts the ＂See and Avoid＂ principle. Under the binding conditions of flight rules, visibility requirements, responding time, the aircraft speed, circle banking angle or the climbing angle, based on its study on aircraft dynamics principles, this paper establishes a mathematical collision avoidance model for head-to-head traffic and crossing converging traffic at the same level. And the safety separation requirements of the aircrafts in low altitude flight are equantitatively analyzed. Finally, the Matlab software is used to analyze the above method. The result shows that the safe traffic avoidance of the converging traffic at the same level meets certain flight conditions, while intersecting the traffic at the same level can safely avoid the collision.

Initial Analysis on the Effect of High-low Altitude Jet Stream on Heavy Precipitation in Guangxi

By using the routine observation data,a heavy precipitation process which happened in Guangxi on May 27,2006 was analyzed.The results that this heavy precipitation occurred in the common coordination weather system which included the high-altitude trough,the shear line and the ground cold front.The ascent branch of subtropical longitude circle circulation and the polar front jet stream longitude circle circulation had the important role for the formation of rainstorm area.The coupling effect of southerly jet,low-altitude westerly jet and high-altitude westerly jet in the boundary layer was the important reason of rainstorm occurrence.

Analysis on the Forecast Characteristics of K Index and Low-altitude Jet Stream in the Rainstorm Process

By using the durative rainstorm data in South China during May-early June in 2010,the forecast characteristics of K index and low level jet were analyzed.The results found that K2 had the good indication,advancement and relativity on the intensity and falling zone forecast of regional rainstorm in future 24 h,and the positive relative coefficient reached 0.987.The low level jet also had the same advancement and indication significance on the intensity and influence scope of regional rainstorm in 24 h in the future,and the relative coefficient reached above 0.8.K2 and the low level jet were selected as the main factors,and the basic conceptual model of rainstorm falling zone was established.The model has passed the computer program and realized the business automation.K2 provided the important basis for the forecast of rainstorm intensity and falling zone.

Algorithm for Low Altitude Penetration Aircraft Path Planning with Improved Ant Colony Algorithm

The ant colony algorithm is a new class of population basic algorithm. The path planning is realized by the use of ant colony algorithm when the plane executes the low altitude penetration, which provides a new method for the path planning. In the paper the traditional ant colony algorithm is improved, and measures of keeping optimization, adaptively selecting and adaptively adjusting are applied, by which better path at higher convergence speed can be found. Finally the algorithm is implemented with computer simulation and preferable results are obtained.

Rapid identification of landslide,collapse and crack based on low-altitude remote sensing image of UAV

Landslides,collapses and cracks are the main types of geological hazards,which threaten the safety of human life and property at all times.In emergency surveying and mapping,it is timeconsuming and laborious to use the method of field artificial investigation and recognition and using satellite image to identify ground hazards,there are some problems,such as time lag,low resolution,and difficult to select the map on demand.In this paper,a10 cm per pixel resolution photogrammetry of a geological hazard-prone area of Taohuagou,Shanxi Province,China is carried out by DJ 4 UAV.The digital orthophoto model(DOM),digital surface model(DSM) and three-dimensional point cloud model(3 DPCM) are generated in this region.The method of visual interpretation of cracks based on DOM(as main)-3 DPCM(as auxiliary) and landslide and collapse based on 3 DPCM(as main)-DOM and DSM(as auxiliary) are proposed.Based on the low altitude remote sensing image of UAV,the shape characteristics,geological characteristics and distribution of the identified hazards are analyzed.The results show that using UAV low altitude remote sensing image,the method of combination of main and auxiliary data can quickly and accurately identify landslide,collapse and crack,the accuracy of crack identification is 93%,and the accuracy of landslide and collapse identification is 100%.It mainly occurs in silty clay and mudstone geology and is greatly affected by slope foot excavation.This study can play a great role in the recognition of sudden hazards by low altitude remote sensing images of UAV.

Relationship between acute high altitude response, cardiac function injury, and high altitude de-adaptation response after returning to lower altitude

The relationship between acute high altitude response (AHAR), cardiac function injury, and high altitude de-adaptation response (HADAR) was assessed. Cardiac function indicators were assessed for 96 men (18 - 35 years old) deployed into a high altitude (3700 - 4800 m) environment requiring intense physical activity. The subjects were divided into 3 groups based on AHAR at high altitude: severe AHAR (n = 24), mild to moderate AHAR (Group B, n = 47) and non-AHAR (Group C, 25);and based on HADAR: severe HADAR (Group E, n = 19), mild to moderate HADAR (Group F, n = 40) and non-HADAR (Group G, n = 37) after return to lower altitude (1,500 m). Cardiac function indicators were measured after 50 days at high altitude and at 12 h, 15 days, and 30 days after return to lower altitude. Controls were 50 healthy volunteers (Group D, n = 50) at 1500 m. Significant differences were observed in cardiac function indicators among groups A, B, C, and D. AHAR score was positively correlated with HADAR score (r = 0.863, P < 0.001). Significant differ- ences were also observed in cardiac function indicators among groups D, E, F, and G, 12 h and15 days after return to lower altitude. There were no significant differences in cardiac function indicators among the groups, 30 days after return to lower altitude, compared to group D. The results indicated that the severity of HADAR is associated with the severity of AHAR and cardiac injury, and prolonged recovery.

Computational mission analysis and conceptual system design for super low altitude satellite

This paper deals with system engineering and design methodology for super low altitude satel ites in the view of the com-putational mission analysis. Due to the slight advance of imaging instruments, such as the focus of camera and the image element of charge coupled device （CCD）, it is an innovative and economical way to improve the camera’s resolution to enforce the satel ite to fly on the lower altitude orbit. DFH-3, the mature satel ite bus de-veloped by Chinese Academy of Space Technology, is employed to define the mass and power budgets for the computational mis-sion analysis and the detailed engineering design for super low altitude satel ites. An effective iterative algorithm is proposed to solve the ergodic representation of feasible mass and power bud-gets at the flight altitude under constraints. Besides, boundaries of mass or power exist for every altitude, where the upper boundary is derived from the maximum power, while the minimum thrust force holds the lower boundary before the power reaching the initial value. What’s more, an analytical algorithm is employed to numerical y investigate the coverage percentage over the altitude, so that the nominal altitude could be selected from al the feasi-ble altitudes based on both the mass and power budgets and the repetitive ground traces. The local time at the descending node is chosen for the nominal sun-synchronous orbit based on the average evaluation function. After determining the key orbital ele-ments based on the computational mission analysis, the detailed engineering design on the configuration and other subsystems, like power, telemetry telecontrol and communication （TT＆amp;C）, and attitude determination and control system （ADCS）, is performed based on the benchmark bus, besides, some improvements to the bus are also implemented to accommodate the flight at a super low altitude. Two operation strategies, drag-free closed-loop mode and on/off open-loop mode, are presented to maintain the satel-lite’s altitude. Final y, a flight planning schedule for the satel ite is demonstrated from its launch into the initial altitude at the very beginning to its decay to death in the end.

Effect of dissolved-oxygen on the flotation behavior of pyrite at high altitude area

With the continuous development of mineral resources to high altitude areas,the study of sulfide ore flotation in unconventional systems has been emphasized.There is a consensus that moderate oxidation of sulfide ore is beneficial to flotation,but the specific suitable dissolved oxygen value is inconclusive,and there are few studies on sulfide ore flotation under low dissolved oxygen environment at high altitude.In this paper,we designed and assembled an atmosphere simulation flotation equipment to simulate the flotation of pyrite at high altitude by controlling the partial pressure of N_(2)/O_(2) and dissolved oxygen under atmospheric conditions.X-ray photoelectron spec-troscopy(XPS),atomic force microscope(AFM),Fourier transform infrared spectrometer(FT-IR),UV-vis spectrophotometer,zeta po-tential,and contact angle measurements were used to reveal the effects of surface oxidation and agent adsorption on pyrite at high altitude(4600 m dissolved oxygen(DO)=4.0 mg/L).The results of pure mineral flotation indicated that the high altitude and low dissolved oxy-gen environment is favorable for pyrite flotation.Contact angle measurements and XPS analysis showed that the high altitude atmosphere nslows down the oxidation of pyrite surface,facilitates S_(n)^(2-)/S^(0) production and enhances surface hydrophobicity.Electrochemical calcula-tions and zeta potential analysis showed that the influence of atmosphere on the form of pyrite adsorption is small,and the different atmo-spheric conditions are consistent with dixanthogen electrochemical adsorption,with lower Zeta potential under high altitude atmosphere and significant potential shift after sodium isobutyl xanthate(SIBX)adsorption.The results of FT-IR,UV-vis,and AFM analysis showed that SIBX adsorbed more on the surface of pyrite under high altitude atmosphere and adsorbed on the surface in a mesh structure com-posed of column/block.The results of the experimental study revealed the reasons for the easy flotation of sulfide ores at high altitude with less collector dosage,and confirmed that the combined DO-pH regulation is beneficial to achieve more efficient flotation of pyrite.

Solar Radiation Penetrating Through Sea Ice Under Very Low Solar Altitude

Based on the optical data for transmitted radiation through sea ice in the Arctic during the late autumn and early winterof 2007,the authors studied the arriving solar radiation,reflected radiation and transmitted radiation under very low solar altitude.Through the atmosphere,the light of the arriving solar radiation at short wavelength was weakened,with the spectral distribution ofdouble peaks centered at 490 nm and 683 nm.The magnitude of the peak at 683 nm even exceeded that at 490 nm under the very lowsolar radiation condition.The reflection was lower than that in summertime because of the thin thicknesses of ice and snow,allowinghigher ratio of heat to enter the sea ice and snow.When higher ratio of solar radiation entered sea ice in late autumn,the new icefreezing would be affected.The spectral reflectivity from snow surface was almost a constant,but the reflection without snow de-creased at longer wavelengths.In the transmission spectrum,the light of 490 nm was dominant.It indicates that the radiation atlonger wavelength was weakened by sea ice.Therefore,under the condition of low solar altitude,the radiation at shorter wavelengthwas weakened by the atmosphere while the radiation at longer wavelength was weakened by the sea ice.The combined effect of at-mosphere and sea ice made the solar radiation under sea ice much weaker.The absorption of sea ice for the longer-wavelength radiation allowed the sea ice to gain more heat to slow down the freezing process.

Soil Physico-Chemical Properties and Different Altitudes Affect Arbuscular Mycorrhizal Fungi Abundance and Colonization in Cacao Plantations of Cameroon

This study aims to investigate the abundance of AMF according to soil properties and altitudes in different cacao plantations of Cameroon. Physico-chemical analyses were made on soil samples collected from three agro-ecological zones. Soil samples were also used to evaluate directly the AMF abundance following the various altitudes and after trapping by sorghum plant. The results showed that soil properties, AMF spore abundances and colonization fluctuated significantly at different altitudes. The most represented texture was sandy loam. The bimodal zone presented a homogeneous texture (sandy loam) in all its localities. Cacao soil chemical characteristics showed that, the highest nitrogen rate (0.47%;p 0.05, Scott-Knott test) was recorded at Melong in a monomodal zone while Tonga in the Western highlands displayed the lowest rate (0.13%). Soil P concentration was significantly high in monomodal zones (Mbanga and Melong). Soil pH level indicated that the soil from Tonga in the Western highlands was neutral (pH = 6.67), and soils of other localities under study were acidic with the lowest (4.75) pH level recorded at Melong in a monomodal zone. In soil samples, the highest spore density (1.03 spores/g soil) was observed at Ntui in Bimodal zone, while the lowest spore density (0.26 spores/g soil) was observed at Bafang in the Western highlands. Root colonization showed that the sample from Bokito in a bimodal zone displayed the best frequency of mycorrhization (86.11%) while the sample from Bafang in the Western highlands recorded the lowest (27.11%). The PCA analysis highlighted that available phosphorus, pH and altitude all strongly correlated with AMF root colonization ability and can be used as a predictor of AMF colonization ability in cacao rhizosphere.

Small-scale alpine topography at low latitudes and high altitudes:refuge areas of the genus Chrysanthemum and its allies

Cultivated chrysanthemum(Chrysanthemum morifolium Ramat.)is an economically important ornamental plant species grown worldwide.However,the origin of the genus Chrysanthemum remains unclear.This study was conducted in the Hengduan Mountains,Yunnan Province.We took advantage of a special geographic region where the southernmost species of Ajania and the highest altitude population of Chrysanthemum indicum coexist to investigate their evolutionary origins.Diversity analysis of 9 populations of 5 species that came from 3 genera was carried out based on morphological traits and SRAP markers.Furthermore,topographical and ecological analyses and surveys of the vegetation communities in the plots were carried out for correlation analysis,and past data were used to reconstruct the ancient topography and vegetation to estimate the migration path and divergence time.We found that Chrysanthemum and Ajania were closely related based on the smooth transition states among marginal female florets and their common pollination system.The genetic relationship between Phaeostigma and Chrysanthemum was relatively distant,and Ajania was between them.Low light intensity and relatively humid habitats may be driving the elongation and evolution of marginal female florets.We found that Chrysanthemum and related genera were largely restricted to stony topographies at an altitude of~3000 m.a.s.l.and in specialized alpine coniferous(Pinus)and broadleaved(Quercus)mixed forest marginal communities.These stony topographies have become ecological islands of refuge for these species in the current interglacial period.The Hengduan Mountains play a key role in the evolution,divergence,and survival of Chrysanthemum and its allies.

The characteristics of negative corona discharge and radio interference at different altitudes based on coaxial wire-cylinder gap

The corona discharge from transmission lines in high-altitude areas is more severe than at lower altitudes. The radio interference caused thereby is a key factor to be considered when designing transmission lines. To study the influence of altitude on negative corona characteristics, an experimental platform comprising a movable small corona cage was established: experiments were conducted at four altitudes in the range of 1120-4320 m, and data on the corona current pulse and radio interference level of 0.8-mm diameter fine copper wire under different negative voltages were collected. The experimental results show that the average amplitude, repetition frequency and average current of the corona current pulse increase with increasing altitude. The dispersion of pulse amplitude increases with increase in altitude, while the randomness of the pulse interval decreases continuously. Taking the average current as an intermediate variable,the relationship between radio interference level and altitude is obtained. The result of this research has some significance for understanding the corona discharge characteristics of ultra-highvoltage lines.

Hydrogen Therapy Reduces Oxidative Stress-associated Risks Following Acute and Chronic Exposure to High-altitude Environment

Low pressure,low oxygen concentration,and intense ultraviolet（UV）radiation in high-altitude environments,can cause oxidative stress which can trigger mountain sickness.A recent study demonstrated that hydrogen gas with a good permeability in biological membranes can treat various disorders by exerting its selective anti-oxidation and anti-inflammatory effects,indicating that hydrogen therapy plays a role in scavenging free radicals and in balancing oxidation and anti-oxidation systems of ceils. Therefore, we hypothesize that inhaling low-dose hydrogen or drinking hydrogen-saturated water is a novel and simple method to prevent and treat oxidative stress injury caused by low pressure, low oxygen concentration and intense UV radiation in plateaus, thus reducing the risk of mountain sickness.

The cardiovascular system at high altitude:A bibliometric and visualization analysis

BACKGROUND When exposed to high-altitude environments,the cardiovascular system undergoes various changes,the performance and mechanisms of which remain controversial.AIM To summarize the latest research advancements and hot research points in the cardiovascular system at high altitude by conducting a bibliometric and visualization analysis.METHODS The literature was systematically retrieved and filtered using the Web of Science Core Collection of Science Citation Index Expanded.A visualization analysis of the identified publications was conducted employing CiteSpace and VOSviewer.RESULTS A total of 1674 publications were included in the study,with an observed annual increase in the number of publications spanning from 1990 to 2022.The United States of America emerged as the predominant contributor,while Universidad Peruana Cayetano Heredia stood out as the institution with the highest publication output.Notably,Jean-Paul Richalet demonstrated the highest productivity among researchers focusing on the cardiovascular system at high altitude.Furthermore,Peter Bärtsch emerged as the author with the highest number of cited articles.Keyword analysis identified hypoxia,exercise,acclimatization,acute and chronic mountain sickness,pulmonary hypertension,metabolism,and echocardiography as the primary research hot research points and emerging directions in the study of the cardiovascular system at high altitude.CONCLUSION Over the past 32 years,research on the cardiovascular system in high-altitude regions has been steadily increasing.Future research in this field may focus on areas such as hypoxia adaptation,metabolism,and cardiopulmonary exercise.Strengthening interdisciplinary and multi-team collaborations will facilitate further exploration of the pathophysiological mechanisms underlying cardiovascular changes in high-altitude environments and provide a theoretical basis for standardized disease diagnosis and treatment.

Association between physiological responses after exercise at low altitude and acute mountain sickness upon ascent is sex-dependent

Background:Acute mountain sickness(AMS)is the mildest form of acute altitude illnesses,and consists of nonspecific symptoms when unacclimatized persons ascend to elevation of≥2500 m.Risk factors of AMS include:the altitude,individual susceptibility,ascending rate and degree of pre-acclimatization.In the current study,we examined whether physiological response at low altitude could predict the development of AMS.Methods:A total of 111 healthy adult healthy volunteers participated in this trial;and 99(67 men and 32 women)completed the entire study protocol.Subjects were asked to complete a 9-min exercise program using a mechanically braked bicycle ergometer at low altitude(500 m).Heart rate,blood pressure(BP)and pulse oxygen saturation(SpO2)were recorded prior to and during the last minute of exercise.The ascent from 500 m to 4100 m was completed in 2 days.AMS was defined as≥3 points in a 4-item Lake Louise Score,with at least one point from headache wat 6–8 h after the ascent.Results:Among the 99 assessable subjects,47(23 men and 24 women)developed AMS at 4100 m.In comparison to the subjects without AMS,those who developed AMS had lower proportion of men(48.9%vs.84.6%,P<0.001),height(168.4±5.9 cm vs.171.3±6.1 cm,P=0.019),weight(62.0±10.0 kg vs.66.7±8.6 kg,P=0.014)and proportion of smokers(23.4%vs.51.9%,P=0.004).Multivariate regression analysis revealed the following independent risks for AMS:female sex(odds ratio(OR)=6.32,P<0.001),SpO2 change upon exercise at low altitude(OR=0.63,P=0.002)and systolic BP change after the ascent(OR=0.96,P=0.029).Women had larger reduction in SpO2 after the ascent,higher AMS percentage and absolute AMS score.Larger reduction of SpO2 after exercise was associated with both AMS incidence(P=0.001)and AMS score(P<0.001)in men but not in women.Conclusions:Larger SpO2 reduction after exercise at low altitude was an independent risk for AMS upon ascent.Such an association was more robust in men than in women.Trial registration:Chinese Clinical Trial Registration,ChiCTR1900025728.Registered 6 September 2019.

Modification of streamer-to-leader transition model based on radial thermal expansion in the sphere-plane gap discharge at high altitude

Historically,streamer-to-leader transition studies mainly focused on the rod-plane gap and low altitude analysis,with limited attention paid to the sphere-plane gap at high altitude analysis.In this work,sphere-plane gap discharge tests were carried out under the gap distance of 5 m at the Qinghai Ultra High Voltage(UHV)test base at an altitude of 2200 m.The experiments measured the physical parameters such as the discharge current,electric field intensity and instantaneous optical power.The duration of the dark period and the critical charge of streamer-toleader transition were obtained at high altitude.Based on radial thermal expansion of the streamer stem,we established a modified streamer-to-leader transition model of the sphere-plane gap discharge at high altitude,and calculated the stem temperature,stem radii and the duration of streamer-to-leader transition.Compared with the measured duration of sphere-plane electrode discharge at an altitude of 2200 m,the error rate of the modified model was 0.94%,while the classical model was 6.97%,demonstrating the effectiveness of the modified model.From the comparisons and analysis,several suggestions are proposed to improve the numerical model for further quantitative investigations of the leader inception.