Target Strength Research Articles

Modeling of bistatic scattering from an underwater non-penetrable target using a Kirchhoff approximation method

A numerical triangulation and transformation into the time domain of a Kirchhoff approximation (KA) method is proposed for the modeling of bistatic scattering from an underwater non-penetrable target. The time domain solution in this approximation can be split up into two parts: the solution of reflected field, contributing around the specular direction, and the solution of shadow radiation, contributing around the forward direction. An average solution in the time domain satisfying the reciprocity principle is presented. The solution is expressed in terms of non-singular functions. The proposed method is validated against a normal mode method for bistatic scattering from a rigid sphere. Moreover, the reflected and shadow highlights on the surface of the sphere are shown to verify the integration surface of the reflected field and shadow radiation. It is also tested against a finite element method and an experiment involving a scaled Benchmark Target Strength Simulation Submarine model. The time-angle bistatic spectra for the model are evaluated by the direct and transformed average solutions of KA, and the former accelerates its speed of calculation. The results are good, and show that this method can be used to predict the bistatic scattered field of a non-penetrable target.

Impacts of Morphological Characteristics on Target Strength of Chub Mackerel (Scomber japonicus) in the Northwest Pacific Ocean

Chub mackerel (Scomber japonicus) is an important commercial fish in the Northwest Pacific Ocean. Accurate target strength (TS) underpins acoustic stock assessment but the TS of S. japonicus is still poorly understood. In this study, the Kirchhoff-ray mode (KRM) model was used to estimate the TS of S. japonicus and its relationship with sound wave frequency and fish morphology. The results revealed that TS values varied with pitch angle shifts, with the impact on fish scattering strength being greater at higher frequency. This is less important because 38 kHz has been used for the biomass assessment of these fish resources. At frequencies of 38 kHz, 70 kHz, 120 kHz and 200 kHz, TS was greatest at a pitch angle range of -10° to 0°, which was related to the angle of the swim bladder tilt. There were almost no differences between TS estimated using the measured pitch angle distributions and using the universal distribution. When the measured pitch angle was N[-3°,4°], the average TS of S. japonicus with body length of 12.04–22.17 cm at four frequencies was -48.88 dB, -49.14 dB, -49.75 dB and -48.55 dB, respectively. The regression intercept (b20) in TS–body length equation was -73.27 dB, -73.56 dB, -74.18 dB and -73.46 dB, respectively. Variation in TS range at 0–300 m depth was about 10 dB. The simulated broadband target strength spectrum shows the scattering characteristics of individuals with different swim bladder length between 0–250 kHz. These results could be used for identification of S. japonicus in echograms and provide reference for acoustic stock assessment of S. japonicus in the Northwest Pacific Ocean.

Beneficial utilization of ultra-fine dredged sand from Yangtze River channel as a concrete material based on the minimum paste theory

Ultra-fine sands are dredged periodically in order to maintain the normal activities of the Yangtze River Channel. Finding a new solution for managing these ultra-fine dredged sand becomes a challenge for channel managers. In this study, ultra-fine dredged sand and manufactured sand were used as the concrete fine aggregates. The concrete mix ratio was obtained based on the minimum paste theory by setting different target strengths, Average Paste Thickness (APT) between aggregates and dredged sand contents. The feasibility of applying the minimum paste theory in the design of ultra-fine dredged sand concrete mix ratio was verified by compressive strength tests. The influences of APT and dredged sand content on the mechanical properties and workability of concrete were analyzed. The results showed that with the increase of the APT, the compressive strength initially was increased and then decreased and the workability was improved. The workability of the concrete was improved with more content of ultra-fine dredged sand through the analysis of the microstructure of the fine aggregates. The concrete with a mass ratio 25% ultra-fine dredged sand had a lower harmful porosity which was verified by mercury intrusion porosimetry (MIP) and SEM, and has a compressive strength value of 43.8 MPa at 28 days which was 11.4% and 10.61% higher than that of the control group with the content ratio of 0% and 50%, respectively. The test results proved that the use of the minimum paste theory in the design of the ultra-fine dredged sand concrete mix ratio is expected to obtain concrete with fewer paste content and proper working performance.

A Prototype Target Strength Measuring System for Small Organisms Using an Acrylic Water Tank

A Prototype Target Strength Measuring System for Small Organisms Using an Acrylic Water Tank

Time frequency investigation and representation of acoustic backscatter signatures

Observation of an object’s structural acoustic response, considered in the aspect-dependent frequency response domain, is a data representation used for characterizing the target strength of an object. Geometric and elastic wave features in the angle-frequency domain are difficult to distinguish. Time varying characteristics such as attenuation are lost with a single frequency transform across the entire time collection of the acoustic return. Research in the aspect angle-frequency domain primarily applies the fast Fourier transform to an entire time series collection for a single ping cycle. This work aims to extend the dimensional space of analysis for the acoustic backscatter representation by investigating time-frequency resolution across aspect angle for acoustic elastic responses of an object. Empirical analysis of the data is presented with application of various time frequency transforms. These methods are assessed using time frequency localization metrics to quantify their performance with the AirSAS dataset. This exploratory work will develop the intuition regarding how the time frequency distribution can be localized, measured, and vary among objects of differing compositions. The ways in which time frequency localization can support distinguishing features of the acoustic return beyond the traditional aspect angle-frequency domain will be discussed as well.

An appraisal of the mechanical, microstructural, and thermal characteristics of concrete containing waste PET as coarse aggregate

• Heat-processed PET-modified concrete is appropriate for strutural applications. • Heat-processed PET-modified concrete is visible, and suitable as it conserves natural resources. • Heat-processed PET aggregate is sustainable as it substitues natural aggregaes with waste plastics. This study assessed the workability, mechanical, microstructural, and thermal behaviours of concrete composed from recycled waste polyethylene terephthalate (PET) as a partial or full replacement for natural coarse aggregates. Workability and Compressive/Split tensile strength tests alongside microstructural and thermogravimetric analysis were performed. Results disclosed that the concrete’s workability increased with increasing percentages of PET. The compressive strength increases with extended curing but decreases as the percentages of waste PET increased at different curing lengths. The PET-modified blends could not yield the target design strength for grade 25 concrete after 28 days. However, the 20% PET-modified mix reached the target strength for concrete grade 20. For all blends, increase in split tensile strength with curing lengths was observed, only the 20% PET-modified blend achieved suitable split tensile strength values. Microstructural analysis revealed that the 100% PET sample has a relatively irregular surface pattern with pores of about 2–4 µm, high quantities of Ca, and minor traces of O, C, Al, Si, Mg, and Na. While PC-20 had a much denser interface between the PET aggregates and the cement matrix with high percentage of Si, O, and Ca, and moderate to minor percentage of Al, Au, Na, and Mg. Thermal analysis showed that the 100% PET sample endured three transition stages. The research outcomes prove that heat-processed PET-modified concrete is suitable for structural applications due to its acceptable fresh, mechanical, microstructural, and thermal properties. Moreover, this alternative is eco-friendly and sustainable as it substitutes natural aggregates with waste plastics.

Using Telehealth to Conduct Family-Centered, Movement Intervention Research in Children With Autism Spectrum Disorder During the COVID-19 Pandemic.

After the COVID-19 pandemic, several randomized controlled trials came to a halt; however, we chose to reinvent our study and shifted to a home-based, telehealth intervention delivery format to support children with autism spectrum disorder and their families. Children with autism spectrum disorder have social communication impairments as well as perceptuomotor and cognitive comorbidities. Continued access to care is crucial for their long-term development. We created a general movement intervention to target strength, endurance, executive functioning, and social skills through goal-directed games and activities delivered using a telehealth intervention model. Our family-centered approach allowed for collaboration between trainers and caregivers and made it easy for families to replicate training activities at home. While more studies comparing telehealth and face-to-face interventions are needed, we encourage researchers and clinicians to consider family-centered telehealth as a valid and feasible intervention delivery method, to increase the likelihood of carryover of skills into the daily lives of children and ultimately enhance their long-term development.

Closed-loop recycling of C&D waste: Mechanical properties of concrete with the repeatedly recycled C&D powder as partial cement replacement

Studies have been conducted on the repeated recycling of recycled coarse aggregates and recycled fine aggregates obtained from concrete waste, but no research has been conducted on the repeated recycling of recycled powder as a partial replacement for cement, which is pointed out as a major source of CO2 in the concrete industry. This paper investigates the closed-loop recycling potential of construction wastes by evaluating the effects of repeated use of concrete powder generated in the production of recycled aggregates on the selected fresh and hardened mechanical properties of concrete. Through a series of concrete making and crushing, once-, twice-, three times-recycled concrete powder of less than 150 μm was collected and used as a partial replacement for cement in concrete matrices at replacement levels of 10%, 20% and 30%. According to the experiment results, the replacement ratio and the number of recycling of concrete powder are parameters that affect the properties of concrete, and in particular, the replacement ratio is more affected than the number of recycling. The strength of concrete containing 10–20% concrete powder surpassed the target strength by up to 21% over three times of recycling, and the cost and environmental benefits increase in proportion to the number of concrete powder recycling. This study can contribute to the valorization of construction waste by providing a new initiative for multi-recycling of concrete powder and a closed-loop recycling system for construction waste.

Experimental Investigation of Engineering Properties of Iron-Based Binary and Ternary Pozzolanic Supplementary Cementitious Materials

The characteristic global warming potential of ordinary Portland cement (OPC) makes it a huge challenge for researchers to weigh its enormous use with potentially feasible engineering properties versus the environmental impacts. The formulation of sustainable, economical, and greener supplementary cementitious materials (SCMs) is an ongoing phenomenon, attracting the large-scale attention of industry/ academia. The formulation of ferrock by David Stone with low embodied energy, lower consumption of natural resources and minimal global warming potential has paved the way for the use of novel material comprising iron powder, pozzolans (pulverised fly ash (PFA) and metakaolin (MK) and lime exhibiting at par performance with OPC. However, a gap has been identified in its formulation, raising a further research question on how it will perform if PFA and MK are replaced by ground granulated blast furnace slag (GGBS) or other pozzolans like silica fume (SF) etc., with different mix ratios. Therefore, an endeavour has been made in this study to identify the engineering properties with sustainable use of modified binary and ternary pozzolans/ GGBS in place of 20% PFA in conventional ferrock. The conventional ferrock contains 8% MK and 20% PFA (as binary pozzolans), 60% iron powder, 12% lime and 2% oxalic acid (set 1). An effort has been made to formulate the different mixes of 10,20,30,40 and 50% by keeping 60% iron powder, 12% lime, 8% MK and 2% oxalic acid constant but replacing 20% PFA with 20% GGBS (set 2), with 10%PFA+10%GGBS (set 3) and with 10%PFA+10%SF (set 4). A target compressive strength of C32/40 or M40 concrete was selected for this study to achieve and compare results with the control mix (0% ferrock) and conventional ferrock during the experimental investigation of modified novel materials. 10-20% ratios of modified mixes exhibited the best performance and achieved the threshold strength of 60 MPa of high-strength cement concrete. Maximum compressive strength of 65 MPa was achieved by the 10% mix of set 2 (20% GGBS), followed by 20% mix ratios of set 3 (10%PFA+10%GGBS) and set 4 (10%PFA+10%SF), achieving 64 MPa. Whereas the 10% mix of the conventional ferrock (set1) reached 63 MPa strength, and the control mix with no ferrock gained 57 MPa strength at 56 days of curing. Overall, an increase of 2-13% compressive strength was observed with10- 30% mixes of all the SCMs; however, a decrease of 3-27% was observed with 40-50% use of SCMs. The use of iron powder increased the ductility of ferrock-based SCMs mixes and exhibited more flexural strength. Set 3 performed the best in exhibiting up to 5.8 MPa flexural strength, followed by set 4, set 2 and lastly, set 1 of conventional ferrock. 20% and 30% mix ratios exhibited flexural strength of more than 5% MPa, better than 10% and 40/ 50% mixes. The study supports the use of 10-20% ferrock-based SCMs for high-strength concrete and 10-50% for concrete mixes with a target strength of C32/40 or M40 to decrease the CO2 footprints of the construction industry significantly.

Experimental and Analytical Study on the Penetration Depth of Mortar Targets Subjected to Projectile Impact in the Hypervelocity Regime

A projectile may be deformed and eroded due to the high pressure generated by hypervelocity penetration, which makes it difficult to describe the penetration mechanism for protection engineering by existing theories at such high velocities. To analyze the penetration depth of concrete-like targets subjected to hypervelocity impact by kinetic energy weapons, experiments with ogive-nosed steel projectiles penetrating mortar targets are conducted, where the average uniaxial compressive strength of the mortar targets is 41.8[Formula: see text]MPa and the impact velocities range from 1[Formula: see text]225[Formula: see text]m/s to 2[Formula: see text]392[Formula: see text]m/s. The experimental results show that the crater diameter and crater depth have a linear relationship with the striking velocity. The depth of penetration (DOP) increases linearly first and then decreases sharply and increases slowly again. Three penetration regimes are observed in turn with increasing velocity, i.e. rigid projectile penetration, abrasive projectile penetration and semifluid projectile penetration. Furthermore, based on a study of the dynamic compression behavior and penetration resistance function of concrete, a hydroelastoplastic-frictional penetration model is established. The velocity range is divided into solid penetration, semifluid penetration and fluid penetration, which correspond to [Formula: see text], [Formula: see text] and [Formula: see text], respectively. Then, the rigid and abrasive projectile penetration models, which consider the projectile mass loss, are verified by the present test data. Finally, the semifluid projectile penetration model is evaluated with the existing test data. These results can provide support for research on the damage effect of hypervelocity kinetic energy weapons and the design of underground strategic protection engineering.

Experimental analyzing the static puncture resistance performance of shear thickening fluid impregnated polypropylene hybrid composite target structures for armour application

The challenges of today’s protective material developers' requirements for body armour target structure design, strength, stiffness, and light weight structures have historically come from composite structures having high cost, complex manufacturing, and time-consuming process. Hence, there is a need to identify suitable alternate materials with reliable composites and essential design requirements for high impact armour structures. At present, hybrid composite structures are increasingly utilized in armour structure developments because they offer quick adoption to produce low cost, high impact strength, and a methodology for easy and quick manufacturing process without compromising the performance of traditional composite structures. This experimental analysis reports that the prepared hybrid composite target structures are composed of woven polypropylene fabric impregnated with single, double, and triple layers with a prepared shear thickening fluid (STF) concentration (50 vol% silica dispersed in polyethylene glycol 600 g/mol) used as a core layer in this structure and a neat/silica gel coated aluminum face sheet is used as the skin material. The prepared STF is characterized through rheological analysis exhibits shear thickening behavior reveals that extensively depends on silica particle morphology, volume fraction, and particle size distribution. The prepared hybrid composite target structure test results demonstrate a significant enhancement in tensile strength, modulus, better peel resistance properties, and puncture resistance evaluated in different geometry of projectiles like flat, hemispherical, elliptical, and conical indentor penetration velocity at 500 mm/min have been performed to demonstrate the improvements in the target structure. It enhances the performance layer thickness increases with increasing puncture resistance for all indentors sequently identified and penetration damage of target structures varied with respect to indentor nose head surface area of contacts.

Analysis of CO2 Emissions from Low Strength Recycled Concrete

In this paper, we determined the calculation boundary of CO2 emissions from low strength recycled concrete, and calculated the CO2 emissions from the low strength recycled broken brick concrete RC15 with the target strength of 15 MPa and the ordinary concrete C15, as well as the proportion of CO2 emissions from each material of the low strength recycled concrete. The results showed that the low strength recycled concrete had less CO2 emissions. The results of the proportion of CO2 emissions from each material of the low strength recycled concrete showed that cement was in the largest proportion and other materials were in a smaller proportion.

Assessing the size spectra of marine fish communities with hydroacoustics: examining the challenges of abundant schools, diverse assemblages, and variable orientations

Assessing marine fish community size spectra with hydroacoustics is challenging, as communities are diverse, schooling and swim-bladder-less fishes are common, and fish orientation is variable. We developed an approach to examine these challenges and applied it to data from 51 optic–acoustic surveys of fishes at petroleum platforms throughout the US Gulf of Mexico. When in situ target strength (TS; dB re 1 m2) distributions were used to calculate the density (and subsequently abundance) of schooling fishes, fish lengths and size spectra slopes were significantly smaller than in simulated communities and fish community censuses at platforms (i.e., reference datasets). However, acoustic slopes were comparable to reference slopes when simulated TS values (based on species composition) were used to calculate schooling fish abundance. These findings held regardless of whether specific or general models were used to convert TS to length. Fish orientation was not a useful predictor of TS or slope, but may explain why in situ TS measurements from small groups of fishes around schools were unsuitable for abundance calculations. By examining the challenges associated with assessing size spectra with acoustics, this study aids progress towards using acoustic size spectra metrics for ecological inferences.

In situ TS detections using two generations of echo-sounder, EK60 and EK80: the continuity of fishery acoustic data in lakes

Used for several decades and recognized today as a reliable method, fishery acoustics is commonly used in scientific studies and monitoring surveys. In Europe, during the last decades, the most frequently used scientific echo-sounder has been the EK60 from the Simrad company (Simrad Kongsberg Maritime AS, Horten, Norway). A new echo-sounder model, the EK80, has been recently developed, and it is therefore necessary to check whether the results obtained by the two generations of echo-sounder (EK60 and EK80) give the same results. This is of main importance in the context of time series. Recent works have already addressed this comparison, focusing on SA (nautical area backscattering coefficient) but the systems' reliability to accurately measuring target strength (TS, in dB) has only been tested using calibration spheres. Our work aims to test the hypothesis that, at a given frequency, the TS recorded simultaneously in situ by an EK60 and an EK80, in CW mode, were not statistically different. Data were recorded in two peri-alpine lakes using the two systems sampling sequentially a similar volume. Using statistical tests, acoustics metrics were compared. For TS, statistically significant differences were found between the two generations of echo-sounder. However, these differences were not large enough to affect the fish density used for fishery management or researches on the fish population. The continuity of the time series acquired with the EK60 is ensured when one switches to the EK80 echo-sounder for lake ecosystem research and monitoring.

Large mesopelagic fish biomass in the Southern Ocean resolved by acoustic properties.

The oceanic mesopelagic zone, 200–1000 m below sea level, holds abundant small fishes that play central roles in ecosystem function. Global mesopelagic fish biomass estimates are increasingly derived using active acoustics, where echosounder-generated signals are emitted, reflected by pelagic organisms and detected by transducers on vessels. Previous studies have interpreted a ubiquitous decline in acoustic reflectance towards the Antarctic continent as a reduction in mesopelagic fish biomass. Here, we use empirical data to estimate species-specific acoustic target strength for the dominant mesopelagic fish of the Scotia Sea in the Southern Ocean. We use these data, alongside estimates of fish relative abundance from net surveys, to interpret signals received in acoustic surveys and calculate mesopelagic biomass of the broader Southern Ocean. We estimate the Southern Ocean mesopelagic fish biomass to be approximately 274 million tonnes if Antarctic krill contribute to the acoustic signal, or 570 million tonnes if mesopelagic fish alone are responsible. These quantities are approximately 1.8 and 3.8 times greater than previous net-based biomass estimates. We also show a peak in fish biomass towards the seasonal ice-edge, corresponding to the preferred feeding grounds of penguins and seals, which may be at risk under future climate change scenarios. Our study provides new insights into the abundance and distributions of ecologically significant mesopelagic fish stocks across the Southern Ocean ecosystem.

Property analysis and mixture design of high ductility cementitious composites with totally recycled fine aggregate based on target strength and strain capacity

The natural fine aggregate was completely substituted by the crushed waste concrete particles with original particle grade in preparing high ductility cementitious composite to promote the waste recycling, reduce the environmental pollution, realize the cleaner production and achieve the better properties in this study. The compressive and uniaxial tensile tests were conducted to analyze the effects of water-binder ratio, fiber volume fraction, recycled fine aggregate-binder ratio and fly ash content on the mechanical properties of high ductility cementitious composites with totally recycled fine aggregate (R-HDCC). The test results showed that the compressive strength of R-HDCC decreased significantly with the increasing of water-binder ratio. The peak tensile stress of R-HDCC was improved remarkably as fiber volume fraction increased and water-binder ratio decreased. The ultimate tensile strain of R-HDCC increased significantly with the increasing of water-binder ratio, fiber volume fraction and fly ash content, whereas reduced with the increasing of recycled fine aggregate-binder ratio. The relationships between the compressive strength, the peak tensile stress, ultimate tensile strain of R-HDCC and corresponding key parameters were set up according to the statistical analysis of test results. Then a mixture design method of R-HDCC based on the target strength and strain capacity was further developed. The detailed procedure of using the proposed mixture design method was illustrated with examples, and the reliability of the method was verified by the experimental results in this study and relevant literatures.

Estimating target strength of young chum salmon (Oncorhynchus keta)

Although chum salmon (Oncorhynchus keta) is an important fishery resource in Japan, acoustic methods cannot be applied to biomass estimation because the target strength (TS) is unknown. This study clarified the TS for each fork length (FL: 5.5–33.5 cm) of young chum salmon inhabiting the Japanese coastal area to the Bering Sea by measuring free-swimming fish. The size dependences of the TS values were TSmean = 20 log10 FL – 68.0, for both 38 and 120 kHz. This facilitated the estimation of biomass of young salmon using acoustic methods.

Partial replacement of cement with alternative cementitious material in the production of concrete: A review

Cement is the main and costliest material in the making of concrete. Also, the cement production is the second largest industrial CO2 source on earth. So, there is need for cement alternative in concrete production to reduce the cement production. This review paper focuses on the use of cementitious materials as a limited substitute for cement in the production of concrete. The use of cementitious material as a partial alternative helps in the making of cost efficient-concrete. The paper summarizes the previous research paper that used cementitious materials like fly ash (FA), metakaolin (MK), silica fume (SF), rice husk ash (RHA), ground granulated blast-furnace slag (GGBS), alccofine, etc. A certain amount of replacement with these cementitious materials with cement have showed good results in terms of strength. The concrete made with these materials showed less mechanical strength compared with conventional concrete but have achieved the required target strength at different time interval. The concrete made with alccofine as a partial replacement had a chloride diffusion because of its natural fine pore structure and its resistance against chemicals showed reduced penetration of chlorides elements into the concrete. Some materials showed, that amount of water required to attain the normal workability as conventional concrete has increased and vice-versa. Finally, it is concluded that the cementitious materials may be used as an alternative to cement for the production of cost and environmentally friendly concrete.

The characteristics of spatial-temporal distributions of fish resources in Lake Jingpo based on hydroacoustic assessment

2020年5、7和10月，采用多网目复合刺网调查和水声学探测相结合的方式对镜泊湖鱼类群落时空动态和资源量进行调查.渔获物调查共采集鱼类4目6科29种，其中鲤科鱼类最多，主要经济鱼类为鲢（Hypophthalmichthys molitrix）、鳙（Aristichthys nobilis）、蒙古鲌（Chanodichthys mongolicus）、瓦氏雅罗鱼（Leuciscus waleckii）、鲤（Cyprinus carpio）、翘嘴鲌（Culter alburnus）.蒙古鲌和（Hemiculter leucisculus）为优势种.水声学探测结果表明，镜泊湖鱼类密度在春季、夏季和秋季分别为836、7216和2724 ind./hm²，其中夏季鱼类密度最高且主要集中于中部和南部区域，春季和秋季鱼类密度则呈现从南至北递减的趋势.春、夏、秋季鱼类的平均目标强度为-43.4、-50.0和-46.5 dB，估算的平均全长分别为34.0、18.0和25.2 cm，推算的平均体重分别为272.7、43.7和135.2 g.结合各季节平均密度，估算出春、夏、秋季镜泊湖鱼类资源量分别为2052、2835和3313 t.镜泊湖鱼类密度与环境因子之间的冗余分析结果表明，水体总悬浮物、叶绿素a、水温和溶解氧是影响鱼类群落结构变化的关键环境因子.从水声学探测和刺网调查的结果来看，镜泊湖渔获物小型化问题突出，鱼类资源呈现衰退趋势，渔业资源的不合理利用是造成镜泊湖鱼类资源衰退的主要因素.因此建议强化对自然捕捞的管理，严格控制捕捞数量和规格，保障鱼类资源自然增殖，结合牡丹江流域污染防治、改善鱼类栖息地环境等鱼类生境修复措施，以促进鱼类资源的恢复.;In May, July and October 2020, a combination of multi-mesh gillnet and hydroacoustic survey was undertaken to investigate the characteristics of spatial-temporal distributions of fish resources of Lake Jingpo. A total of 29 fish species, belonging to four orders and six families, were collected during the survey. The main economic fish are Hypophthalmichthys molitrix, Aristichthys nobilis, Chanodichthys mongolicus, Leuciscus waleckii, Cyprinus carpio, and Culter alburnus. The dominant species are Chanodichthys mongolicus and Hemiculter leucisculus. The average fish density was 836 ind./hm² in spring, 7216 ind./hm² in summer and 2724 ind./hm² in autumn. In summer, fish mainly inhabited in the central and southern regions. In spring and autumn, the species density showed a decreasing trend from the south to the north. The average target strengths were -43.4, -50.0 and -46.5 dB in spring, summer and autumn, the estimated average total lengths 34.0, 18.0 and 25.2 cm, and the estimated average weights 272.7, 43.7 and 135.2 g, respectively. The estimated average density of fish resources in Lake Jingpo was 2052, 2835 and 3313 t in spring, summer and autumn, respectively. The results of redundancy analysis between the fish density and environmental factors in Lake Jingpo showed that the total suspended solids, chlorophyll-a, water temperature and dissolved oxygen were the key environmental factors affecting the changes of fish community structure. According to the results of hydroacoustic and gillnet survey, the problem of miniaturization of catches in Lake Jingpo is prominent, and the fish resources are declining. Irrational utilization is the main factor resulting in the decline of fishery resources in Lake Jingpo. We recommend the relevant authorities strengthen the management of natural fishing strictly control the number and size of fishing, ensure the natural proliferation of fish resources, and integrate the pollution control of the Mudanjiang River Basin and the improvement of fish habitat environment and other fish habitat restoration measures, in order to promote the recovery of fishery resources.

Effect of compression casting technique on the water absorption properties of concrete made using 100% recycled aggregates

Effect of compression casting technique on the water absorption characteristics of low grade 100% Recycled Aggregate Concrete (RAC) of target strength range 11 to 15 MPa to be used in the manufacturing of masonry units is investigated. Water absorption characteristics were determined by performing sorptivity test. Recycled aggregates were produced by crushing laboratory-tested concrete samples of strength ranging from 21 MPa to 28 MPa. Two different ratios of recycled coarse aggregate and recycled fine aggregates were investigated using two different cement contents. For comparison, natural aggregate concrete mixes were also tested. The study parameter included effect of aggregates type, casting pressure, casting technique and cement content on the water absorption properties of RAC. Further, depth of penetration of salt was observed using silver nitrate solution after 3-month immersion in 10% NaCl solution. The results of sorptivity test showed positive impact of compression casting technique on water absorption properties of low grade 100% RAC. Further, results showed that RAC mixes exhibited inferior water absorption properties compared to natural aggregates concrete mixes. Various equations were proposed to predict water absorption of 100% RAC under different conditions of casting pressure and cement content based on initial and secondary rate of water absorption.