A Compact Low Frequency Vivaldi Antenna for Ground Penetrating Radar

One of the most important parts in ground penetrating radar (GPR) system is the antenna. To transmit the waves to deep depths, the operating frequency should be decreased as possible. A compact Vivaldi antenna is proposed with operating frequency of 0.4 GHz and dimensions of (0.26λ_o×0.21λ_o×0.002λ_o), where λ_o is the free-space wavelength at the operating frequency. To increase the gain of the Vivaldi antenna, the length of antenna should be increased. The conventional Vivaldi antenna length should be greater than λ_o. In order to improve the gain of the Vivaldi antenna while maintaining a compact size, a triple slot line structure is proposed. The Vivaldi antenna is etched on a thin economic substrate (FR4) with permittivity of ε_r=4.4 and thickness of h=1.6 mm. ith permittivity of ε_r=4.4 and thickness of h=1.6 mm. ith permittivity of ε_r=4.4 and thickness of h=1.6 mm. ith permittivity of ε_r=4.4 and thickness of h=1.6 mm

A Compact Low Frequency Vivaldi Antenna for Ground Penetrating Radar

One of the most important parts in ground penetrating radar (GPR) system is the antenna. To transmit the waves to deep depths, the operating frequency should be decreased as possible. A compact Vivaldi antenna is proposed with operating frequency of 0.4 GHz and dimensions of (0.26λ_o×0.21λ_o×0.002λ_o), where λ_o is the free-space wavelength at the operating frequency. To increase the gain of the Vivaldi antenna, the length of antenna should be increased. The conventional Vivaldi antenna length should be greater than λ_o. In order to improve the gain of the Vivaldi antenna while maintaining a compact size, a triple slot line structure is proposed. The Vivaldi antenna is etched on a thin economic substrate (FR4) with permittivity of ε_r=4.4 and thickness of h=1.6 mm. ith permittivity of ε_r=4.4 and thickness of h=1.6 mm. ith permittivity of ε_r=4.4 and thickness of h=1.6 mm. ith permittivity of ε_r=4.4 and thickness of h=1.6 mm

Study a Structural Behavior of Eccentrically Loaded GFRP Reinforced Columns Made of Geopolymer Concrete

This study investigated a modern composite material, which is a short geopolymer concrete column (GPCC) reinforced by GFRP bars. The structural performances of GPCC subjected to eccentric load were studied and compared to the normal strength concrete column (NSCC) reinforced by steel bars. In this study, the primary experimental parameters were the reinforcement bars types, load eccentricity, and concrete types. Seven short columns were tested: three normal strength concrete columns reinforced by steel bars, three geopolymer concrete columns reinforced by GFRP bars and one normal strength concrete column without reinforcement. The model dimensions chosen in the present study was a square section of 130×130 mm and a total height of 850 mm. It was shown that the steel bars contribute about 16.47% of column capacity under concentric load. Comparing with the normal strength concrete column, a geopolymer concrete column reinforced by GFRP bars showed a little increase in ultimate load (5.17%) under concentric load. Under the load eccentricity of 130 mm, a geopolymer concrete column reinforced by GFRP bars showed a significant increase in the ultimate load (69.37%). Under large eccentricity, a geopolymer concrete column reinforced by GFRP bars has an outstanding effect on the columns' ultimate load capacity. Also, the sine form can be utilized for GPCC to find the lateral deflection along with the column high at different load values up to the failure

STR-837: PUNCHING SHEAR BEHAVIOUR OF HIGH STRENGTH CONCRETE SLAB-COLUMN CONNECTIONS REINFORCED WITH GFRP BARS

The catastrophic nature of punching shear failure exhibited by flat plate system requires a great attention and robust predictions of the behaviour of slab-column connections. This paper presents an experimental study carried out to investigate the punching shear behaviour of fibre-reinforced polymer (FRP) reinforced concrete (RC) interior slab-column connections made of high strength concrete (HSC). Three full-scale HSC specimens were constructed and tested up to failure. The three connections were reinforced with GFRP sand-coated bars with reinforcement ratios of 1.0, 1.5 and 2.0% without any shear reinforcement. The typical dimensions of the test specimens were 2800 × 2800 × 200 mm with a 300 mm square column extending 1000 mm above and below the slab, representing the region of negative bending moment around an interior supporting column of a parking structure. All specimens were simply-supported along all four edges with the corners free to lift. The connections were subjected to vertical load and unbalanced moment that were monotonically applied through the column tips. The behaviour of the specimens in terms of the deformation and strength characteristics is discussed. Increasing the reinforcement ratio increased the punching shear capacity and decreased the reinforcement strains and deflections at the same load level. The test results were also compared to the predictions of the relevant North American codes where applicable

Uterine sparing approaches in management of placenta accreta: a summarized review

Placenta accreta is a potentially life-threatening obstetric condition that required multidisciplinary approach to management. Placenta accreta occurs in complete absence of the decidua basalis. Women with previous cesarean section delivery or placenta previa are known to be at greater risk of placenta accreta. A previous study reported that 24%& 67% increase in the incidence of placenta accreta in women 1 versus 3 or more previous cesarean deliveries respectively. Antenatal diagnosis of placental invasion has the potential to improve maternal and fetal outcomes. In practice, incomplete non-separation of the placenta at delivery leads to massive obstetric hemorrhage resulting in maternal morbidities such as massive blood transfusion, DIC, injury to the bladder and intestines and the need for hysterectomy. Sonographic examination with gray scale and color doppler imaging is the recommended first line modality for diagnosis of morbidly adherent placenta. Techniques developed for conservative management are techniques developed to preserve uterus and future fertility which is crucially linked to societal status and self-esteem

Prediction of preterm birth by evaluating the fetal adrenal gland volume and blood flow: a pilot study

Background: The aim of the current study was to estimate the risk of preterm birth (delivery < 37 weeks of gestation) by evaluating the fetal adrenal gland volume and blood flow at Women’s Health Hospital, Assiut University, Egypt.Methods: A pilot prospective cohort study included pregnant women presented to our hospital with threatened preterm labor between December 2016 and May 2018. All women were recruited consecutively at the emergency unit of Women’s Health Hospital at Assiut University. The fetal adrenal gland volume was assessed using 3-dimensional images of the fetal adrenal with the aid of Virtual Organ Computer-Aided Analysis (VOCAL) software. Doppler evaluation of the fetal adrenal blood vessels was carried out. The RI, PI and S/D ratio was calculated for every case. The neonatal outcomes at delivery were assessed and compared with respect to the duration of actual delivery from the time of evaluation. The obtained data were analyzed by SPSS software (version 22.0) and p<0.05 was taken as the significant level.Results: The study included 30 pregnant women at the final analysis. Women were classified according to the time of actual delivery into two groups. Group (I, n=13) those who delivered within 7 days and group (II, n=17) those who delivered 7 days or more. No difference between both groups regarding the baseline characteristics. No difference regarding the mode of delivery (p=0.708). All Doppler indices were statistically in-different between both groups. The fetal adrenal gland volume was significantly lower in group II than group I (p=0.001). On ROC analysis, the area under the curve (AUC) for prediction of preterm birth based on the fetal adrenal gland volume was (AUC= 0.873). The ROC curve shows that the best cut off value using the volume was ≥0.461 with 76.92% sensitivity and 88.24% specificity for prediction of preterm birth with an overall accuracy of 83.3%.Conclusions: Fetal adrenal gland volume was identified as a significant predictor of delivery in pregnant women who had spontaneous preterm births with intact membranes

Dislocation Microstructure and Surface Roughness Evolution in Single and Multi-phase Microcrystals

A better understanding of the plastic deformation of metallic materials and their failure can greatly accelerate future material development. However, attaining such an understanding is difficult through only experimental investigations and/or simple analytical models. Recent advances in coarse grained simulations using large scale discrete dislocation dynamics (DDD) simulations provide detailed spatio-temporal descriptions of the evolution of complex dislocation networks in crystals having arbitrary microstructures and initial defect distributions, and under different loading conditions. In this thesis, a DDD framework has been developed and utilized to investigate the evolution of dislocation microstructures and surface roughness in single and multi-phase metal microcrystals. First, three atomistically identified cross-slip mechanisms, namely, bulk, intersection and surface cross-slip, have been implemented in the DDD framework and utilized to study monotonic axial deformation in single crystal Nickel microcrystals of different sizes and initial dislocation densities. It is concluded that cross-slip leads to significant dislocation density multiplication, strain hardening, the formation of dislocation cell-like structures in larger crystals and the formation and thickening of slip bands on the crystal surface. Surface cross-slip was found to be the most frequent, followed by intersection and then bulk cross-slip. These simulations are also shown to be in agreement with recent microcompression experimental observations in both Nickel and Aluminium microcrystals. Second, the evolution of dislocation microstructure and surface roughness during cyclic mechanical loading was investigated. The cyclic response was divided into two separate stages: the early stage response starting from a random dislocation microstructure, and the response of crystals having well-developed Persistent Slip Band (PSB). In random dislocation microstructure simulations, crystals having sizes larger that 5 μm showed cyclic hardening, significant dislocation density multiplication and the formation of dislocation cell-like structures. The evolution of surface roughness due to dislocations escape has been quantified. The atomic concentration of point defects generated from dislocation annihilation in PSB walls was quantified and was found to agree with experimental estimates. Finally, the DDD framework was extended to model the interaction of dislocations with an arbitrary distribution of precipitates that have an L12 crystal structure by explicitly tracking the creation and destruction of Anti-Phase Boundary (APB) regions. This framework was then utilized to perform the first DDD simulations of single crystal superalloy micropillars with different precipitate microstructures. The micropillar strength was found to vary linearly, follow a square-root relationship and an inverse square-root relationship with the precipitate volume fraction, APB energy and size respectively while the crystal size has no effect on its strength. The width of the inter-precipitate channels was found to be the main strength determining factor. The results were validated with detailed comparisons with recent microcompression experiments on single crystal Nickel-based superalloys