Middle Bar Research Articles

Gravity-guided snapping sequence in 3D modular multistable metamaterials

The snapping sequence of multistable metamaterials is critical for their applications in elastic wave control and energy release. Despite being a fundamental property, the effect of gravity on the snapping sequence has never been studied. This paper investigates the mechanical mechanism how structural gravity affects the snapping sequence of multistable metamaterials to construct deterministic static and dynamic snapping sequences. A biaxial snap-through availability three-dimensional (3D) modular multistable metamaterial (MMM) is developed. The 3D MMM is assembled from unit cells consisting of a dismountable middle bar (M-bar) and a fixed frame containing two bistable curved beams. Except experimental tests and numerical simulations, analytical analyses are also conducted to verify the snapping sequence induced by gravity in the 3D MMM. In addition, given that the M-bar is dismountable, the effects of its length on the mechanical properties and the impact resistance of the 3D MMM are discussed in detail. It is found that gravity can guide both static and dynamic deterministic snapping sequences of the 3D MMM to optimize the process of elastic wave propagation and energy release, and the proposed 3D MMM can enhance structural impact resistance through elastic deformations.

The investigation of an inspired type toroidal dipole flexible metasurfaces at terahertz frequencies

We theoretically and experimentally carried out an inspired type of toroidal dipole (TD) metasurfaces, which composed of a metamolecule of symmetric aluminium semicircles with a bar in the middle fabricated on polyimide substrate in the terahertz (THz) regime. It was found that the three resonances show red-shift tendency due to the increase of inductance and capacitance with the increase of semicircle's outer radius. Meanwhile, both the TD resonances and the current flowing in the metallic bar can generate the head-to-tail magnetic field distribution, which is the most prominent feature of TD phenomenon. The generation of this phenomenon is discussed deeply via the power of the multipoles, which are calculated according to the volume current density distribution data extracted from the simulations. The low frequencies (∼0.5 THz) head-to-tail magnetic field distribution is mainly attributed to TD resonance generated via the mutual effect between the two semicircles, while the same phenomenon at high frequencies (∼0.8 THz) is mainly attributed to the current flowing the middle metallic bar. The enhancement of head-to-tail magnetic field distribution leads to the increase of quality (Q) factor, and the Q factor of fabricated sample is as high as 24.5. Moreover, the electromagnetic properties in TD metasurfaces could be adjusted by the metal bar's width. The optimization of TD resonances provides opportunity to design the high Q-factor metasurfaces, and it opens up potential applications in terahertz high sensitivity devices.

Study on static performance and dynamic characteristics of a spoke cable-truss suspen-dome system

The proposed spoke cable-truss suspen-dome structure is a new structure system based on the traditional chord-supported dome structure. In this structure, the upper lattice shell is modified to a radial cable-truss structure. The lower part of the structure is a cable network structure composed of radial cables, ring cables and radial cables. There are few research results on the mechanical properties of the new structure, so a 1:10 scale model is established, multi-condition static loading test, local cable force failure test and natural vibration characteristic test are carried out, and the measured results are compared with the finite element results. The changes of axial force and joint displacement under different loads, the changes of static properties under cable damage and the dynamic characteristics of the structure are obtained. The results show that the loading method adopted meets the test accuracy requirements. Under the action of uniform load, the upper chord, the lower chord end and the inner ring truss of the main truss are in a pure compression state. The middle bar of the lower chord span and the outer ring truss change from the compression state to the tension state with the increase of load. The structure is still in the elastic stage when part of the cable fails, and the coordinated deformation ability is strong. The base frequency of the measured structure is 7.97 Hz, and the stiffness distribution is uniform.

Four Years of Meander‐Bend Evolution Captured by Drone‐Based Lidar Reveals Lack of Width Maintenance on the White River, Indiana, USA

AbstractMeandering rivers experience fluctuations in width whenever riverbanks migrate in different directions or at different rates, which can be observed after individual floods. However, meandering rivers maintain approximately constant widths over decadal timescales. This implies some timescale below which width fluctuates as banks migrate independently, and above which width is maintained by a bank‐coupling process. This coupling is thought to occur either as point bar deposition events induce cutbank erosion (bar‐push), or as cutbank erosion events induce point bar deposition (bank‐pull). This coupling, however, has been challenging to observe in natural rivers due to limited event‐scale field data. We present results from a 4.5‐year campaign with 22 drone‐based lidar surveys of a single point bar and cutbank (∼0.35 km2 in area) on the White River near Worthington, Indiana, USA. The middle point bar experienced net erosion (5,400 m3), but net aggradation (17,100 m3) between 2019 and 2022 when including perennially submerged regions. This aggradation was less than the 35,700 m3 of cutbank erosion over the same period. Combined, we have observed widening (1.58 m/yr bend‐averaged; 3.08 m/yr near apex) over the study period as point bar deposition has not kept up with cutbank erosion. Finally, we suggest that the difference between bar‐push and bank‐pull as width‐maintenance mechanisms may not be resolvable by observing bend widening or narrowing alone without an advancement of current theory, such as determining a long‐term equilibrium width and measuring deviations relative thereto.

Experimental Study on Mechanical Properties of Reinforced Soil and Frame Beam Anchor Combination System

To address issues with excessive displacement, deformation, and insufficient load bearing capacity in high-fill-reinforced soil-retaining walls, a novel reinforced soil–frame anchor combination system was developed. Despite the limited existing research on its mechanical properties and synergy, a physical model test was conducted to investigate the system’s behavior. The test focused on the horizontal displacement of the frame beam wall, grid strain, wall back earth pressure, and anchor strain. Results indicated that anchor prestress effectively controlled horizontal deformation, limiting it to 65% of the original displacement value. Additionally, as the top load increased, strain in the bottom bars showed minor changes, while strain in the middle and upper bars exhibited significant sensitivity to load variations. The application of anchor prestress reduced strain in each reinforcement layer, enhancing the geogrid’s load bearing capacity. Furthermore, anchor prestress altered the distribution of earth pressure within the system, establishing a synergistic relationship between reinforced soil and frame beam anchors. This stress transfer mechanism improved overall system performance, as demonstrated in the test. Overall, the study confirmed the benefits and superior performance of the combined system.

Experimental study on flexural performance of composite slabs with bent bars and postcast ultrahigh‐performance concrete joints

AbstractThis paper describes the use of joints with bent bars and postcast ultrahigh‐performance concrete (UHPC) joints to enable formwork‐free and support‐free construction of composite slabs. To investigate their flexural performance, static loading tests on three full‐scale simply‐supported slabs and one monolithic slab were carried out. Flexural capacity, stiffness, and crack development were recorded, resulting on flexural failure experienced by all specimens. Main cracks of composite specimens developed along the UHPC–normal concrete interface, and cracks on both sides of the UHPC joint developed evenly, similar with that of the monolithic specimen. Besides, composite slabs and a monolithic slab showed similar flexural capacity. UHPC joint was not cracked when failure occurred, and bottom bars were anchored and connected in the UHPC joint, proving that the flexural anchorage method is feasible. The average strain of the composite specimen across the UHPC joint was still consistent with the assumption of plain section, and there was an approximate linear relationship between the expansion width of the joint at the bottom of the slab and the maximum crack width at bottom bars. Moreover, middle bars contributed to the flexural capacity and stiffness of composite specimens, while horse stool reinforcement may effectively prevent the interface shear failure on the composite interface. Based on test results, the formula to control cracking of UHPC is given in this paper. The design methods on flexural capacity, stiffness, and expansion width of composite slabs are also presented and discussed.

Experimental study on the corrosion characteristics of steel bars in concrete considering the effects of multiple factors

In this paper, twenty reinforced concrete specimens were designed for accelerated corrosion test, and a systematic study was conducted to investigate the effects of water-cement ratio, thickness of concrete cover, and spacing and quantity of steel bars on the corrosion characteristics of steel bars. The results showed that the mass loss of steel bars approximately increased with the water-cement ratio and decreased with an increase in the thickness of concrete cover. As the spacing between the steel bars in lower layer of the specimens increased, the mass loss of the steel bars in lower layer approximately showed an increasing trend. When there were more than two steel bars arranged in lower layer of the specimens, the mass loss of the middle steel bars was smaller than that of the steel bars located in the corner areas on both sides. The probability distribution type of the corrosion depth was mainly normal distribution, and the influence of water-cement ratio, thickness of concrete cover, and spacing and quantity of steel bars in lower layer of the specimens on the probability distribution was not obvious. The probability distribution type of the width of corrosion-induced cracks was mainly exponential distribution, and the influence of the spacing and quantity of steel bars in lower layer on the probability distribution was not obvious. When the water-cement ratio was large, the width of corrosion-induced cracks was less discrete from its mean value. With the increase of the quantity of steel bars in lower layer, the shape of the probability distribution curve of the width of corrosion-induced cracks tended to be flat. There was a good positive linear relationship between the mass loss of steel bars and the average width of corrosion-induced cracks, and the influence of water-cement ratio and the spacing between the steel bars in lower layer on this linear relationship was irregular. A good positive linear relationship between the maximum width of corrosion-induced cracks and the average corrosion depth of steel bars was established, which was irregularly affected by the water-cement ratio and the spacing between the steel bars in lower layer.

Gold prices, cultural factors, and Covid-19 pandemic: An international analysis

Using data from 24 economies from 2010 to 2022, we demonstrated the significant effect of national culture, a missing factor, on physical, jewellery, and gold bar and coin demand. We also determined that the COVID-19 pandemic variable has a significantly positive influence on demand for gold in Confucian economies, jewellery in South Asian and Middle East economies, and bar and coin in Confucian economies. One key implication is that although the total global gold consumption tends to decline during economic turmoil, individuals in these countries tend to accumulate more gold because gold is considered as a safe haven asset during the Covid-19 pandemic. Our findings also provide useful implications for the development of the gold markets.

Declassified intelligence satellite imagery as a tool to reconstruct past landforms and surface processes: The submerged riverscape of the Tigris River below the Mosul Dam Lake, Iraq

AbstractLocated along the Tigris River in the Kurdistan Region of Iraq, the Mosul Dam Reservoir is the second biggest dam of the Near East and represents an important water storage for local human activities. The dam was built between 1981 and 1988 north of the village of Eski Mosul, submerging the course of the Tigris River for c. 100 km. The analysis of historical images derived from declassified Corona satellite imagery acquired between December 1967 and August 1968 reveals the pristine pattern of the Tigris River, including the seasonal changes of its riverbed, shifting across the hydrological year from meandering to anastomosing patterns. Geomorphological mapping based on Corona images allowed us to estimate the seasonal modification of fluvial elements such as the floodplain and point, middle and longitudinal bars. The comparison with Landsat data collected since the 1990s showed the first phases of the basin filling and the control on the present‐day aspect of the lake inherited from the setting of the Tigris channel belt and, more in general, the litho‐structural control over the evolution of the local hydrographic network; we also document the influence of the original Tigris River course on its recent insertion into the lake. Our work allowed reconstruction of the ancient fluvial landscape below the Mosul Dam Lake and the evolution of its riverscape controlled by litho‐structural factors and seasonal variations of the river discharge. Finally, this contribution highlights the relevance of declassified intelligence satellite imagery in interpreting natural geomorphic processes and landforms, today altered by human agency.

Analysis of Evolution of Coupled Lorentz Resonances and Their Sensing Properties in Terahertz Metamaterials

Combined with experimental and simulated results, the resonances and metamaterial-induced transparency have been theoretically investigated using the Lorentz oscillator model for terahertz metamaterials with unequal-length bar structures. The bar spacing has an impact on the spectral evolution, implying that the coupling between metal bars varies correspondingly in one unit cell and the adjacent cells. Different from the evidence that the strongest coupling occurs in double bar structures when the bar spacing is uniform in the entire sample, the coupling in 3 bar structures is more complicated due to the weakened coupling with the middle bar and increased coupling between the other 2 bars by further increasing the bar spacing. The dependence of calculated transmission spectra on the damping rate and coupling coefficient is demonstrated, showing that the fitting parameters could control and tune the resonant dips, the transparency peaks, and even the quality factors of the spectra regularly. Furthermore, the sensing properties have been investigated by simulating the spectral evolution with the overlayers of different refractive indices to optimize the sensing parameters. Our obtained results could advance the understanding of resonance coupling and offer the possibility to further study the modulation and biosensing in the coupled terahertz devices.

Experimental investigation of stirrup confinement effects on bond-slip responses for corner and middle bars

Stirrup confinement on bond between concrete and reinforcement is vital for RC (reinforced concrete) structures as it strengthens the friction and mechanical interlock between the two kinds of materials. In this paper, an experimental study has been carried out to look into the stirrup effects on bond-slip responses of RC with corner embedded reinforcing bars and bars embedded in the middle area of cover (corner and middle bars). This aims to quantify the difference of the bond strength caused by the embedment position of reinforcement while confined with hooked and straight stirrups. Different material properties have also been considered in the experiment including concrete cover, bar diameter and stirrup diameter. The failure modes for different specimen groups are presented and discussed. Besides, the influence of stirrup confinement effects on global load-slip response is also investigated by conducting another experiment with long embedment length of reinforcing bars which also includes the corner bars and middle bars. Furthermore, the debonding resistance compared with yielding force of the reinforcing bars are compared and analyzed for the global load-slip responses with stirrup confinements.

Experimental fire testing of large‐scale glass fibre‐reinforced polymer‐reinforced concrete beams with mid‐span straight‐end bar lap splices

SummaryAdopting glass fibre‐reinforced polymer (GFRP) rebars as a replacement of conventional steel reinforcement in different infrastructure applications is mainly attributed to its corrosion resistance and considerable lightweight‐to‐high strength ratio. However, the use of FRP rebars in construction is still limited due to the degradation of its mechanical properties at elevated temperatures. The experimental work presented in this paper aimed to investigate the structural fire behaviour of concrete beams reinforced with GFRP bars having lap splices at the beam mid‐span. Four identical 2750‐mm long concrete beams with cross‐sectional dimensions of 300 mm × 350 mm were experimentally examined under four‐point flexure bending. A 60‐mm thick concrete cover was used on the bottom, front and back sides of all beams. Two beams were tested as control specimens in ambient condition, while the other two beams were exposed to standard fire while subjected to a transverse load equivalent to 40% of the beam ultimate design moment. Experimental results show that concrete beams sustained the applied loads for a minimum of 53 minutes in standard fire conditions. Also, both test beams failed due to slippage of the spliced bars when the temperature measured at the top of the middle bar approached its glass transition temperature.

Analysis of reinforced concrete plates with swimmer bars as punching shear reinforcement

Reinforced concrete flat plates are used in buildings and garages. Their design is governed by deflection at the serviceability limit state and punching shear at the ultimate limit state. A new system of punching shear reinforcement consisting of top and bottom steel cages connected through small inclined bars, called swimmer bars, was studied. The objective of the study was to evaluate this system using non-linear finite-element (FE) analysis. FE models were first calibrated based on experimental work carried out previously. A parametric study was then conducted to study the effect of the inclination angle of the swimmer bars, the number of steel pyramids and the number and location of swimmer bars. The results obtained were compared to those predicted by BS EN 1992-1-1:2004 and ACI 318-14. The results of the parametric study indicated that the optimum inclination angle of the swimmer bars was 45°. The first pyramid of swimmer bars assembly had the highest contribution to punching capacity. It was also found that the swimmer bars located at the corners were more effective than the middle bars; accordingly, middle bars could be eliminated and larger corner bars could be used. Finally, the shear legs and swimmer bars were simulated to compare their performance under punching shear.

三峡水库坝下江心洲植物群落及其性状对不同水淹强度的响应

三峡水库的运行，改变了其坝下游的水沙情势，使坝下游沙洲生境呈现出明显的水淹强度梯度变化。阐明这一梯度变化下沙洲植被组成、分布和性状结构特征，是理解植被与沙洲稳定关系的基础，更是阐明三峡工程对长江中下游地区生态环境影响的核心内容之一。选取上荆江河段第一个江心洲-太平口心滩作为研究样地，通过植被组成和分布特征的调查，对不同水淹强度下群落物种组成、多样性和功能特征进行了深入分析。结果表明：太平口心滩植被组成以草本植物为主，稀布小型灌木川三蕊柳。调查共记录物种21科33属39种，以禾本科和菊科植物为主要优势种。轻微（20-40 d）和极强水淹强度（100+d）条件下的生境物种组成同其他水淹强度生境具有显著性差异，轻微水淹强度下牛鞭草和节节草为主要优势种，极强水淹强度下虉草为主要优势种。不同水淹强度下物种多样性指数差异显著，功能多样性指数和生物多样性指数趋势基本一致。随着水淹时间的延长，植被更倾向于表现出花果期位于出露期、植株高度更加低矮、须根系、进行营养繁殖的功能性状。江心洲植被的群落结构和功能性状特征都在水淹梯度下呈现出明显的梯度变化特征。这些研究结果表明水淹强度的梯度变化是沙洲植物群落变化的重要驱动因子，为进一步研究沙洲植物群落动态变化以及沙洲植被协同演替机制，明晰大坝影响下的生态环境变化提供重要依据。;The composition and distribution characteristics of vegetation play a vital role in the development and stability of the sandbars. Operation of the Three Gorges Reservoir has changed the hydrological and sediment transport regimes in the downstream of the dam, causing a significant gradient on the sandbar habitats along the flooding durations. To clarify the composition, distribution, and structural characteristics of vegetation in the sandbar is fundamental for understanding the roles of vegetation in stabilizing the sandbar. In addition, they provide key information to clarify the relationship between the Three Gorges Project and the ecological and environmental problems in the middle and lower reaches. In this study, we selected the first sandbar, the Taipingkou Middle bar in the upper Jingjiang river section, and used the equidistant systematic sampling plots to investigate the vegetation composition and distribution characteristics. Based on the elevation information of plots and the water level data over the years, we set the plots at 5 flooding gradients levels by the flooding days in a flooding cycle:20-40 d, 40-60 d, 60-80 d, 80-100 d, and over 100 d. Statistical methods, such as importance value, species diversity index, functional diversity index and functional traits analysis, were used to analyze the species composition, diversity and functional traits of communities under different flooding duration days. The results showed that the vegetation composition was dominated by herbaceous plants, and the small shrubs Salix triandroides were sparsely distributed. A total of 39 species, belonging to 21 families and 39 genera, were recorded and the main dominant families were Poaceae and Compositae. The species composition of habitats under intermediate level (20-40 d) and maximum flooding intensity (100+ d) condition is significantly different with that found in other flooded gradients. Under the intermediate flooding intensity, Hemarthria sibirica and Equisetum ramosissimum are the main dominant species, and Phalaris arundinacea is the main dominant species under the maximum flooding intensity. Along the flooding gradient, species diversity is significantly varied. Species richness is low in both intermediate and maximum flooding intensity habitats, but the highest species diversity in the intermediate flooding condition habitats and the lowest in the maximum strong flooding intensity habitats. Basically, the trend of functional diversity index keeps same with biodiversity index, while the functional diversity index under maximum flooding conditions is not representative. As increasing of intensity of flooding stress, the vegetation tends to show the functional traits with flowering and fruit stage under the outcrop stage, while plant height reduction, fibrous root system and vegetative reproduction also show difference. The community structure and the functional traits of the sandbar plants showed obvious gradient change with the flooding gradient. The results show that the gradient change of flooding duration is an important driver shaping sandbar plant community, and provides an important basis for further research on the dynamic succession of sandbar plant community and vegetation succession mechanism of sandbar, and clarifying the ecological environment changes under the influence of dams.

Relationship of point bar morphology to channel curvature and planform evolution

Point bars are prominent features in meandering rivers, yet our understanding of the complex interactions among the morphology of the point bars to channel planform and curvature remains incomplete. This study seeks to address the extent to which channel centerline curvature can explain point bar morphology. High-resolution elevation datasets obtained from multibeam sonar and structure-from-motion surveys are used to characterize point bar morphology on twelve point bars within two river systems; the Pearl and Wabash rivers. Spatial series of centerline curvature are compared to channel and point bar characteristics including width, migration rate, centerline longitudinal bed elevation, transverse bed slope, and a shape factor. Results show that the Wabash reach has overall lower channel curvature values and higher rates of migration compared to the Pearl reach. However, the spatial lag between curvature and width and migration rate are similar between reaches. The mode of bend migration differs between the two reaches, where the Pearl reach has bends mostly evolving through translation downstream, and along the Wabash reach, one bend is expanding, two bends are mostly stationary, and three bends are translating downstream. The translating bends in both reaches exhibit bilinear (a pronounced break in slope) and near-horizontal (a pronounced break in slope with a nearly flat bar top) transverse bar profiles and maximum rates of migration downstream of the apex. The Pearl reach has a systematic distribution of transverse bar profiles where linear profiles are found along the bar head and bar tail, and near-horizontal profiles are concentrated along the middle bar. The distribution along the bars of the Wabash reach is less systematic, with fewer near-horizontal profiles overall. Finally, to evaluate the influence of curvature on the channel bed and bar morphology, the field data are compared to synthetic bed elevation data generated using pyRiverBed, a centerline curvature-driven bed evolution model that maintains a constant width. Analyses reveal the synthetic morphologic data agree reasonably well with the characteristics and magnitude of the field observations, with a mean absolute error of 0.9 and 1.2 m for the Pearl and Wabash rivers, respectively. Values of transverse slope were also compared between the field and synthetic data and the synthetic data are consistently under-predicted along the Pearl. Differences observed between the field and synthetic data are the result of variability in the natural river system not captured by the model including channel width, the presence of local bedrock outcrops, and abrupt changes in curvature.

A New Methodology for the Multilayer Tight Oil Reservoir Water Injection Efficiency Evaluation and Real-Time Optimization

It is important to determine the reasonable injection and production rates in the development of multilayer tight oil reservoir with water flooding treatment. Based on the INSIM (interconnection-based numeric simulation model), a connected network model, a new method is designed to evaluate the water injection efficiency of different layers in water flooding reservoirs and to optimize the injection-production system to produce more oil. Based on the types of sedimentary facies and corresponding injection-production data, the interwell connections are divided into four major categories (middle channel, channel edge, middle channel bar, and channel bar edge) and twelve subclasses. This classification standard of interwell connections could help to significantly improve the accuracy of judging the dominant flow path without constructing a complicated geological model. The interaction of interwells such as injection-production correlation and water injection efficiency could be revealed by simulating the production performance and computing the layer dividing coefficient and well dividing coefficient. A numerical example is used to validate this method by comparing results from FrontSim and this method, and the computational efficiency of this method is several dozen times faster than that of the traditional numerical simulation. This method is applied to quickly optimize the production schedule of a tight oil reservoir with the water flooding treatment, that is, the water injection rate of multilayer reservoirs could be optimized subtly by the injection efficiency of different layers, and the target of producing more oil with lower water cut could be achieved.

The plate body: 3D ultrastructure of a facultative organelle of alveolar epithelial type II cells involved in SP-A trafficking

Plate bodies are facultative organelles occasionally described in the adult lungs of various species, including sheep and goat. They consist of multiple layers of plate-like cisterns with an electron dense middle bar. The present study was performed to elucidate the three-dimensional (3D) characteristics of this organelle and its presumed function in surfactant protein A (SP-A) biology. Archived material of four adult goat lungs and PFA-fixed lung samples of two adult sheep lungs were used for the morphological and immunocytochemical parts of this study, respectively. 3D imaging was performed by electron tomography and focused ion beam scanning electron microscopy (FIB-SEM). Immuno gold labeling was used to analyze whether plate bodies are positive for SP-A. Transmission electron microscopy revealed the presence of plate bodies in three of four goat lungs and in both sheep lungs. Electron tomography and FIB-SEM characterized the plate bodies as layers of two up to over ten layers of membranous cisterns with the characteristic electron dense middle bar. The membranes of the plates were in connection with the rough endoplasmic reticulum and showed vesicular inclusions in the middle of the plates and a vesicular network at the sides of the organelle. Immuno gold labeling revealed the presence of SP-A in the vesicular network of plate bodies but not in the characteristic plates themselves. In conclusion, the present study clearly proves the connection of plate bodies with the rough endoplasmic reticulum and the presence of a vesicular network as part of the organelle involved in SP-A trafficking.

Effect of Different Seasons on the Royal Jelly Production Under Nasr City Conditions – Cairo - Egypt

The study was executed at apiary of Plant protection Dept. Fac. of Agric. Al-Azhar Univ., Cairo, Egypt, during two successive years 2019 and 2020 to determine the effectiveness of different seasons on the acceptance rates of the larvae and royal jelly production. In the first year, the highest acceptance means for Italian hybrid 72.1 and 65.43% for Carniolan hybrid were recorded at mid-spring on the other hand, the lowest acceptance percentages means were 50.86 and 55.8 % recorded at early summer for Carniolan and Italian hybrids respectively. Also, results demonstrated that mid spring gave the best mean weight of royal jelly per queen cell cup 238.35 mg. for Italian hybrid and 236.31 mg. for the Carniolan hybrid. The lowest quantity means were recorded in early summer 187.24 mg./cup for Carniolan hybrid and 198.74 mg./cup for Italian hybrid. In the second year, the highest acceptance means were 66.42 and 62.96% at mid spring for Italian and Carniolan hybrids respectively. Whereas the lowest acceptance percentage means were 44.44 and 48.4 % at early summer for Carniolan and Italian hybrids. Also, results cleared that mid-spring gave the best mean weight of royal jelly per queen cell cup, 229.71 mg. for Italian hybrid and 227.5 mg. for Carniolan hybrid. The lowest quantity means were recorded at early summer 186.72 mg./cup for Carniolan hybrid and 189.06 mg./cup for Italian hybrid. As for the effect of the bar level, the middle bar level gave the best results for royal jelly quantity and cup acceptance while the upper level gave the least royal jelly quantity and acceptance percentages in different seasons. There was a significant difference in acceptance percent and the royal jelly production per cup cell between mid-spring and early summer. Mid-spring gave the best results while the early summer gave the least results.

Riverbed Changes of the Uppermost Atchafalaya River, USA—A Case Study of Channel Dynamics in Large Man-Controlled Alluvial River Confluences

River confluences are important nodes for downstream sediment transport and geomorphological development. Previous studies have established the knowledge that under natural conditions, river confluence zones experience channel scour followed with middle channel bar development. Less care is however given to the intensity of a confluence scour zone under man-controlled conditions, such as discharge regulation and levee confinement. In general, our knowledge about long-term bed evolution downstream of large alluvial river confluences is limited. Here we conducted a study focused on the 69-km uppermost channel of the Atchafalaya River, the largest distributary of the Mississippi River, to test the hypothesis that the channel downstream of two large tributaries sustains longer-term, extensive bed scouring owing to increased discharge in the main channel and, therefore, mid-channel bars in such a confluence zone cannot be built under confined channel conditions. The Atchafalaya River carries the total flow from the Red River and approximately 25% of the Mississippi River flow, traveling southwards 230 km before emptying into the Gulf of Mexico. We utilized long-term records on water surface elevation and discharge during 1935–2016, as well as channel bathymetry survey data during 1998–2006 to determine changes in hydraulic head and morphologic deformation in the confluence zone. The results from this study show that the combined flow from the Red River and Mississippi River into the Atchafalaya River steadily increased to approximately 5848 cubic meters per second (m3 s−1) in the recent decades, and the channel bed of the uppermost Atchafalaya River experienced considerable erosion since the 1930s. At a specific discharge of 8000 ± 100 m3 s−1, the river stage decreased by 5.8, 5.6, and 4.9 m from 1935 to 2016 at (from upstream to downstream) Simmesport, Melville, and Krotz Springs gauging stations, respectively. The average bed elevation reduced by 1.9 m from 1998 to 2006, although its thalweg increased by 0.3 m. Based on the channel bed assessment, a total volume of 6.6 × 107 m3 sediment was eroded from the uppermost 69 km of the Atchafalaya over the 8 years. The findings suggest that confluence zones of large alluvial rivers under controlled flow and confined levee conditions can experience extensive, long-lasting channel erosion. This can be especially progressive if the channel below a confluence is confined by levees, which can increase drag forces and prevent middle channel deposition. Further studies are needed to determine if the eroded sediment from the uppermost Atchafalaya is carried out to the river mouth or is deposited in the lower Atchafalaya. Such knowledge will have both scientific and practical relevance in river engineering and management.

Wave motion over stratified porous absorber combined with seaward vertical barrier

The oblique wave reflection by horizontally stratified porous absorber having two horizontal porous bars of different porosities and friction factors placed on step-type bottom is studied using eigenfunction expansion method based on linearised wave theory. The present study examines several structural configurations such as porous absorber consisting of finite and semi-infinite thickness with/without seaward vertical barrier. The present study derived the direct analytical relations to determine wave reflection by each of the structural configuration for plane-wave assumption using potential flow theory. Initially, the porous absorber considering uniform porosity and friction factor is examined and validated with available numerical results, and the direct analytical relations are also validated with available relations of possible structural configurations. In addition, the present study reported wave reflection performance of submerged single-layer and double-layer porous absorbers with/without seaward vertical barrier. The effect of bottom rigid bar, surface porous bar, middle porous bar depth, multiple porosities, friction factors, incident wave angle and porous effect parameter on wave reflection coefficient is presented in detail for various structural configurations. The significance of seaward vertical barrier on wave reflection and wave trapping is reported. The point of wave trapping, critical angle of impinging, resonating peaks and troughs due to various structural configurations are presented against structural thickness.