Neutron Diffraction of Large-Volume Samples at High Pressure Using Compact Opposed-Anvil Cells

Neutron diffraction techniques of large-volume samples at high pressure using compact opposed-anvil cells are developed at a reactor neutron source, China＇s Mianyang research reactor. We achieve a high-pressure condition of in situ neutron diffraction by means of a newly designed large-volume opposed-anvil cell. This pressure calibration is based on resistance measurements of bismuth and the neutron diffraction of iron. Pressure calibration experiments are performed at room temperature for a new cell using the tungsten carbide anvils with a tapered angle of 30°, Φ4.5 mm culet diameter and the metal-nonmetal composite gasket with a thickness of 2 mm. Transitions in Bi（Ⅰ–Ⅱ 2.55 GPa, Ⅱ–V 7.7 GPa） are observed at 100 and 300 kN, respectively, by resistance measurements.The pressure measurement results of neutron diffraction are consistent with resistance measurements of bismuth.As a result, pressures up to about 7.7 GPa can routinely and stably be achieved using this apparatus, with the sample volume of 9 mm^3.

Function of large-volume high-pressure apparatus at SECUF

Pressure allows the precise tuning of a fundamental parameter, the interatomic distance, which controls the electronic structure and virtually all interatomic interactions that determine material properties. Hence, pressure tuning is an effective tool in the search for new materials with enhanced properties. To realize pressure tuning on matter, large-volume press （LVP） apparatuses have been widely used not only to synthesize novel materials but also to implement the in situ measurement of physical properties. Herein, we introduce the LVP apparatuses, including belt-type, cubic anvil, and 6-8 type multi-anvil, that will be constructed at the Synergetic Extreme Condition User Facility （SECUF） at Jilin University. Typically, cell volumes of 1000 mm3 can be obtained at 20 GPa in a belt-type apparatus that is significantly larger than that obtained in a 6-8 type multi-anvil apparatus at the same pressure. Furthermore, the in situ measurement of physical prop- erties, including thermological, electrical, and mechanical behaviors, is coupled to these LVP apparatuses. Some typical results of both synthetic experiments and in situ measurements obtained from the LVP apparatuses are also reviewed.

Selected Changes in the Microclimate Parameters inside the Large-Volume Buildings Caused by the Heat Emission from People

The paper shows selected aspects of the microclimate change inside the selected type of the large-volume buildings--sacral buildings and for comparison--in the residential apartment buildings, caused by the heat emitted by people. Microclimate parameters such as air temperature or air relative humidity change because of heat emission from people staying inside there. Exemplary methods and results of research conducted in the existing sacral buildings and in the residential apartment buildings are shown. It is based on author＇s research, whose novelty is the research of the human heat emission in case of a big number of people staying inside a large-volume building. It can be useful for sacral buildings and other large-volume buildings design and for a microclimate shaping. In some large-volume buildings as the sacral buildings with a big number of people staying inside at the same time heat emitted from people significantly influences on a microclimate. Human heat streams can be useful as a part of the heat balance of the room.

Characteristics of Airgun Signals Excited in the Yangtze River from Analysis of Data from Permanent Stations

The Anhui Experiment, a pilot experiment of "Yangtze River Geoscience Project "conducted in October,2015,is a large active-source experiment using airgun sources. It was the first 3-dimensional seismic survey with active sources in the Yangtze River. The sources are airguns in 20 fixed shot points,and the observation system consists mainly of109 permanent stations and 11 wide-angle profiles. Using the data from permanent stations,we investigated the seismic signals generated by airgun sources in the Yangtze River. The results show that the airgun signals are observable in the records from permanent stations to a maximum distance of 300 km. Further analysis on absolute amplitude of airgun signals shows that:( 1) the strength of airgun signals is of the order of10 nm at 50 km away from the source,and then,decreases significantly to less than 1nm at 200 km;( 2) an azimuthal anisotropy is observed in spatial distribution of the strength of airgun signals,which may be related to the geometry of Yangtze River; and( 3) a low ambient noise level is essential for retrieving weak airgun signals from the records,and the high-quality China National Seismic Network and regional networks offer a great opportunity to retrieving airgun signals with amplitude as small as nanometers.

Attenuation Characteristics of Earthquake Ground Motion for Large Volume Airgun

In order to further deepen the understanding of seismic wave propagation characteristics induced by the large volume airgun source,experimental data from multiple fixed excitation points in Fujian Province were used to obtain the equivalent single excitation high signal-to-noise ratio velocity and displacement records through linear stacking and simulation techniques.Then the peak displacements of different epicentral distances were used to calculate the equivalent magnitude of the airgun source excitation at different fixed excitation points so as to establish the attenuation relationship between equivalent magnitude,epicenter distance and velocity peak.Our results show that:①Within 270 km of epicentral distance,for the large-volume airgun’s single shot,the peak velocity range is about 700-4 nm/s,and the peak displacement range is about 200.0-0.2 nm;②The equivalent magnitude of the P-wave from the airgun source with a total capacity of 8,000 in 3 is 0.181-0.760,and the equivalent magnitude of the S-wave is 0.294-0.832.By contrast,the equivalent magnitude of the P-wave from the airgun source with a total capacity of 12,000 in 3 is 0.533-0.896,and the equivalent magnitude of the S-wave is 0.611-0.946.The S-wave energy is greater than the P-wave energy,and the excitation efficiency varies greatly with different excitation environment;③The peak velocity increases with the equivalent magnitude,and decreases with the epicentral distance.The vertical component of the P-wave peak velocity is the largest among those three components,while the S-wave has the smallest vertical component and similar horizontal components.Hence,our research can provide an important basis for the quantitative judgment of the seismic wave propagation distance using the airgun and the design of the observation system in deep exploration or monitoring with airgun.

Drainage of ascites in cirrhosis

For cirrhotic refractory ascites,diuretics combined with albumin and vasoactive drugs are the first-line choice for ascites management.However,their therapeutic effects are limited,and most refractory ascites do not respond to medication treat-ment,necessitating consideration of drainage or surgical interventions.Con-sequently,numerous drainage methods for cirrhotic ascites have emerged,including large-volume paracentesis,transjugular intrahepatic portosystemic shunt,peritoneovenous shunt,automated low-flow ascites pump,cell-free and concentrated ascites reinfusion therapy,and peritoneal catheter drainage.This review introduces the advantages and disadvantages of these methods in different aspects,as well as indications and contraindications for this disease.

Influencing factors of seismic signals generated by un-tuned large volume airgun array in a land reservoir

Un-tuned large volume airgun array in a water reservoir is recently proposed as a new way to generate seismic waves on land. It can be used to explore the earth velocity structure and its temporal variations as well. However, the characteristics of seismic signals （especially far-field signals） from an airgun array in a reservoir and its affecting factors （firing pressure, airgun towing depth, water level of the reservoir, etc.） has not been adequately studied. We analyzed the seismic data collected from field experiments at Binchuan Transmitting Seismic Station in 2011 and 2013 and found that （1） The similarity of seismic signals decrease with distance, which is most likely induced by the decay of signal amplitude and signal to noise ratio （SNR）; （2） The amplitudes of far-field airgun signals are almost linearly proportional to the firing pres- sure; （3） The towing depth far-field signals; （4） The signals are proportional to of airgun has less effects on the amplitudes of far-field airgun the water level of the reservoir.

Improving Airgun Signal Detection with Small-Aperture Seismic Array in Yunnan

Repeating airgun sources are eco-friendly sources for monitoring the changes in the physical properties of subsurface mediums,but their signals decay quickly and are buried in the noises soon after traveling short distances.Stacking waveforms from different airgun shots recorded by a single seismic station(shot stacking)is the most popular technique to detect weak signals from noisy backgrounds,and has been widely used to process the data of Fixed Airgun Signal Transmission Stations(FASTS)in China.However,shot stacking sacrifices the time resolution in monitoring to recover a qualified airgun signal by stacking many shots at distance stations,and also suffers from persistent local noises.In this paper,we carried out several small-aperture seismic array experiments around the Binchuan FAST Station(BCFASTS)in Yunnan Province,China,and applied the array technique to improve airgun signal detection.The results show that seismic array processing combining with shot stacking can suppress seismic noises more efficiently,and provide better signal-to-noise ratio(SNR)and coherent airgun signals with less airgun shots.This work suggests that the array technique is a feasible and promising tool in FAST to increase the time resolution and reduce noise interference on routine monitoring.

The Seasonal Variation of Large Volume Airgun Signals in Hutubi,Xinjiang

In order to study the seasonal variation of large volume airgun signals in Hutubi,Xinjiang,we analyzed 2,936 signals of airgun source excitations during 2015-2016 received by a seismograph on the bank of the excitation pool.Firstly,the RMS value of the signal amplitude and the daily average temperature were compared after linearly superimposing the signal in days,to analyze the influence of the surface ice cover on the excitation energy release of the airgun source.The result shows that the ice cover will reduce the excitation energy,and the thicker the ice cover is,the more obvious the excitation energy reduces.Secondly,the time-frequency analysis method was used to analyze the influence of the surface ice cover on the signal frequency.It is concluded that the existence of the ice cover has little effect on the signal frequency,but it will affect the intensity of the signal around 4 Hz between 1-2 s after excitation.The cause of these phenomena is that the ice cover affects the bubble oscillation,which in turn affects the energy conversion.The study shows that when using the cross-correlation delay method to calculate the wave velocity,the signals can be divided into two periods according to the daily average temperature:with or without ice cover on the upper surface of the excitation pool.This can help eliminate the influence of the source variation and improve the accuracy of the monitoring results.

Regional Scale Seismological Investigation on the Continent Crust Using Airgun Sources——A Perspective Review

The investigations on the structure and temporal variations of the continent crust have been the long-lasting topics of seismology. The artificial sources play the most important role in these studies for their well-known locations and occur times among all the sources producing elastic waves,so that precise results are obtained. In past decades,we have successfully excited the airgun sources in on-land water bodies such as reservoirs,expanding their applications in marine seismology. Large volume airguns have been used to produce low frequency signals which can travel hundreds of kilometers after stacking,providing a source connecting the exploration seismology and traditional seismology at regional scale. In this review,we introduce the changes through which we turn the airgun into scientific instruments by experiments. We also present the advances on imaging the continental crust structure and monitoring the velocity variations using the highly repeatable signals emitted by airgun sources. The potential applications such as imaging the subsurface of urban areas and high resolution illuminating of mines are proposed and the challenges for further investigations are also discussed.

Characteristics of Seismic Wave Propagation in the Binchuan Region of Yunnan Using a Dense Seismic Array and Large Volume Airgun Shots

The Binchuan region of Yunnan is a structurally complex region with mountains,basins,and active faults.In this situation,seismic wave propagation exhibits complex characteristics due to strong heterogeneity of underground media instead of following the great-circle path.In order to obtain a high-resolution shallow crustal structure,a dense seismic array was deployed during March 21 to May 30,2017 in this area.To better understand the complexities of seismic wave propagation in this region,we perform array-based frequency-domain beamforming analysis and single-station based polarization analysis to investigate the characteristics of seismic wave propagation,using airgun-generated P-wave signals recorded by dense array stations in this experiment.The results from these two methods both reveal similar but complex characteristics of seismic wave propagation in the Binchuan basin.The azimuth anomalies off the great-circle path are quite large with values up to 30°,which is caused by strong structural heterogeneity in the very shallow crust.Our research provide a better understanding of the complex geologic structures in this area and provide guidance for detecting concealed faults and distribution of velocity anomalies.

Study of the Change in Wave Velocity Ratio before and after Two Strong Earthquakes Using Airgun Source Data

Using the signals excited by the large-volume airgun source at the Binchuan transmitting seismic station from January to June,2016,arrival-time data was acquired at four stations near the epicenter of the Eryuan MS4.5 and MS4.0 earthquakes on February 8,2016,as well as the epicenter of the Yunlong MS5.0 and Eryuan MS4.6 earthquakes on May 18,2016 through the waveform cross-correlation technique.The wave velocity ratio of the four stations was calculated using the single-station method.At the same time,the b-value and the focal mechanism consistency parameters of the study area were also calculated.The results show that:(1)the wave velocity ratio of each station experienced a process of decline-recovery-fast rise before the two strong earthquakes,and a significant quasi-synchronous rapid rise occurred within 3-12 days before the earthquake;(2)the timing of the rapid rise of the wave velocity ratio of the four stations before the Yunlong MS5.0 and Eryuan MS4.6 earthquakes were related to the epicentral distance.The station which observed the earliest increase in rapid rise is the farthest one from the epicenter,and the station where the rapid rise appeared in the latest is closest to the epicenter;(3)the form of change of the wave velocity ratio before the earthquake was different between stations located at different directions in the epicenter area;(4)the b-value and the focal mechanism consistency parameter which is commonly used to characterize the stress level both showed a downward trend before the two strong earthquakes,and were consistent with the change in the wave velocity ratio.According to the preliminary analysis,the wave velocity ratio obtained by using airgun source can better reflect the change in the stress state of the underground medium.

Nonstationary inversion-based directional deconvolution of airgun array signature

Airgun arrays are widely used in marine seismic exploration because signatures excited by airgun arrays have high energy and high-peak bubble ratio, whereas the considerable length and width of the array and ghost reflections make the airgun array signature directional. As a result, the relation of the reflection amplitude with the incident and azimuth angles is variable. This means that the directivity of the airgun array results in a nonstationary wavelet and distorts the relation of the amplitude variation with the incident and azimuth angles. To remove the directivity effect, we propose a nonstationary inversion-based directional deconvolution. At fi rst, the signature as a function of take-off angle and azimuth angle is calculated using the spatial configuration of the airgun array and the near-field signatures. Then, based on the velocity model, the time-variant take-off angles are estimated and directional fi lters are designed using the take-off angles. Finally, the directivity-dependent signatures are shaped to the signature right below the airgun array using nonstationary inversion in the directional deconvolution.

Study on the Influence of Airgun Excitation Conditions on Airgun Signals and Travel Time Variation Measurements

Because of the different excitation conditions of the airgun source,there will be subtle differences in airgun signals.Travel time variation of airgun signals often mix into source information which can’t fully reflect the evolution of the medium.This article uses the airgun signals from the Binchuan Transmitting Seismic Station to analyze the airgun signal′s characteristics of phase and correlation.We conducted a comparative analysis of the effects of the pair difference method and the deconvolution method on eliminating the influence of the excitation conditions in travel time variation.The results show that:(1)The pressure pulse and its subsequent wave of airgun source wavelet are less affected by excitation conditions that we can use it to obtain high-precision excitation moments.(2)Deconvolution can improve the correlation of the airgun signal.(3)The pair difference method can’t eliminate the influence of excitation conditions in travel time variation.Deconvolution can reduce excitation condition interference and the influence of the excitation condition in the travel time variation after deconvolution of the vertical signal is significantly reduced.

Research on Large Volume Airgun Source Signal Reception in Hutubi, Xinjiang Using Seismic Network Data

We used data from the Xinjiang Digital Seismic Network and PSD( Power Spectral Density) method to perform noise level assessment for six stations. We calculated the median of the power spectral density to evaluate the noise level of different stations. After the comparison of the power spectral density of different stations and the airgun signal recognition,we found that noise level of stations with recognizable airgun source signals is lower than that of stations without recognizable signals. The largest difference of the power spectral density is 40 d B,and the smallest is 15 d B. Finally,we found that the failure to recognize the signal of airgun sources at some stations is due to the noise level.

Signal Detection of Large Volume Airgun Source Excitation in the Fixed Field of the Yangtze River

As this is the first time a large volume airgun has been excited in the "Yangtse River Geoscience Project",it is necessary to study the time-frequency characteristic based on the linear stacked seismic data from records from portable stations near the fixed fields and seismic stations. Airgun signal propagation distances were detected using stacked seismic data to analyze the environmental impact on signal propagation distance. The results showed that:( 1) the airgun signal produced by bubble pulses,pressure pulses and the surface wave can be received by a portable station near the fixed field;( 2) the dominant frequency of a bubble at 5Hz or so can be received by both near-field stations and far-field stations,pressure pulses rapidly weaken and the dominant frequency bands get narrower as epicentral distance increases;( 3) the longest spread distance of signal is 260 km,the nearest is 180 km,and the signal can travel further in the evening.

Using Airgun Source Signals to Study Regional Wave Velocity Changes before and after the Yunlong M_S5.0 and Yangbi M_S5.1 Earthquakes

On the basis of the airgun source signals recorded by the stations from January,2016 to June,2017,we use cross-correlation detection technology to obtain the characteristics of the stable phase travel time change of each station.We used the Yunlong MS5.0 and Yangbi MS5.1 earthquakes as samples.According to regional characteristics,13 stations with high signal-to-noise ratios and complete data were selected(including 3 fixed stations and 10 active source stations).They are divided into four regions,and on the basis of the GNSS baseline data,the characteristics of regional wave velocity changes before and after the earthquake are analyzed.The results show that the station phase travel time change and the regional stress characteristics represented by the GNSS baseline data have good correlation in the short-term.Due to different degrees of regional stress,there are differences in the travel time changes of different stations in the four regions.Before the Yunlong MS5.0 and Yangbi MS5.1 earthquakes,with regional stress adjustment,there is an upward trend in the travel time changes of related stations in the adjacent areas of up to 0.02 s.The difference is that there are differences in the time nodes and duration of the travel time anomalies,and there is a reverse descent process after the Yangbi MS5.1 earthquake.There are different degrees of travel time fluctuations in the relevant stations before and after the two earthquakes,but the fluctuation range before and after the earthquake was small.Compared with the water level change of the reservoir,the adjustment of the regional stress is more likely to have a substantial impact on the travel time changes of the relevant stations.

Numerical Simulation of the Binchuan Airgun Source Affected by Water Body

The numerical simulation of the influence of a reservoir water body on the Binchuan airgun source could provide a theoretical basis to analyze the data obtained from the active source detection and inversion of regional interior medium structures.Based on a medium model containing limited water body,we use the finite different method to simulate the effect of the water level,excitation energy and focal depth.The results show that the influence on the waveform amplitude caused by the water level changing is very large near the water body,and that a high water level or large amplitude change can have a larger effect.However,for stations beyond a certain epicentral distance,the influence will be weakened and kept stable.As for the Binchuan airgun source,amplitude fluctuation caused by the water level changing becomes very small(±0.05 times)after propagating a certain distance,so we can remove the influence of the water level changing by referring to the numerical simulation result.Wave amplitude increases linearly with the excitation energy and focal depth,therefore,the greater the energy and the deeper the focal depth,the better the effect of the excitation,and is more conducive in detecting remote and deep penetration underground structures.

Preliminary Results of Tomography from Permanent Stations in the Anhui Airgun Experiment

In order to explore the ability of airgun sources in imaging the crustal structure,we conducted an experiment along the Yangzte River at the section from Ma 'anshan to Anqing using an offshore airgun source( referred as the Anhui Airgun Experiment).During the experiment,the airgun source was fired 2973 times at 20 multiple shot points,while 109 permanent stations and 700 temporary stations( 11 profiles) were used to record the signal. For 20 multiple shot points,we picked up 335 P-wave arrivals at 52 permanent stations. Then we obtained the P-wave velocity structure of the crust beneath the southern tip of the Tancheng-Lujiang( Tan-Lu) fault. The preliminary result of P-wave velocity structure confirms the possibility of 3D body wave imaging using large volume airgun sources. The imaged velocity heterogeneity at a depth of 15 km is correlated to the geological settings. High velocity anomaly beneath the Qinling-Dabie orogenic belt could be explained by the ultrahigh-pressure metamorphic rocks in the deep region,while the low velocity anomaly at the Yangtze River region may correspond to the special background of mineralization.

Study on the Source Characteristics of Downhole Airgun with Different Excitation Environments

The measurement of underground medium variation using a repeated artificial source has gradually become an important goal to pursue. In recent years,we have developed and improved a technology system with large capacity airguns excited in land reservoirs by transplanting marine seismic exploration technology. The excitation effect has a close relationship to airgun capacity,water environment,and excitation conditions. In view that large capacity airgun must be excited without a water environment,we expand the system to use in downhole. Based on the BHS-2200 LL downhole airgun with a capacity of250in3,this paper carries out a comparative analysis on the characteristics of an airgun source excited in 0. 2m- and 5. 0m-diameter wells,and the results show that:( 1) The dominant frequency of the airgun signal excited in a 5. 0m well is mainly from 10 Hz to40Hz,lower than that in a 0. 2m well,and the larger body of water is good for bubble oscillation.( 2) In terms of exciting energy,the signal excited in a 5. 0m well has stronger energy than in a 0. 2m well,with a difference of 1 order in magnitude,and the signal can be detected up to 9km excited in a 5. 0m well with a single shot.( 3) The airgun signal has good repeatability in both excitation wells. The downhole airgun excitation technology system has potential application in dynamic monitoring near a fault zone with a small scale range, exploration of oil and mineral resources, and modern urban geophysical environment.