Numerical modelling of ground penetrating radar for optimization of the time-zero adjustment and complex refractive index model

Time-zero adjustment or the true ground surface for Ground Penetrating Radar (GPR) applications is a very important aspect and an essential factor in order to carry out accurate shallow depth measurements. As the transmitted and received signals from GPR antennas are affected by the presence of different materials with various dielectric constants and electromagnetic properties adjusting the time-zero appropriately is important. This study uses a realistic Three Dimensional (3D) numerical model of a GPR transducer in order to examine where is the best location for time-zero on a GPR trace. It is shown that in order to establish a robust and consistent time-zero position careful consideration is needed also of the way the two-way travel time of the reflected GPR wavelet is estimated as well. Starting with a simple homogeneous model with a set of different targets a better process of time-zero adjustment and time picking of the GPR wavelets is put forward that is verified using further more complex and realistic heterogeneous models. Further verification is obtained by using experimental data. Estimating the permittivity of heterogeneous mixtures based on the permittivity of their individual components is of high importance with many applications in GPR and in electrodynamics-based sensing in general. The Complex Refractive Index Model (CRIM) is the most mainstream approach for estimating the bulk permittivity of heterogeneous materials and has widely been applied for GPR applications. The popularity of CRIM is primarily based on its simplicity while its accuracy has never been rigorously tested. In the current study, an optimized shape factor is derived that is fine-tuned for modelling the dielectric properties of concrete. The bulk permittivity of concrete is expressed with respect to its components i.e, aggregate particles, cement particles, air-void and volumetric water fraction. Different combinations of the above materials are accurately modelled using the Finite-Difference Time-Domain (FDTD) method. The numerically estimated bulk permittivity is then used to fine-tune the shape factor of the CRIM model. Then, using laboratory measurements it is shown that the revised CRIM model over-performs the default shape factor and provides with more accurate estimations of the bulk permittivity of concrete. Numerical modelling of a heterogeneous concrete model and a bowtie antenna with a separate transmitter and receiver that are able to move independently are also presented in this study. Both models are used for the optimisation of the time-zero position and the CRIM model shape factor

Optimising the complex refractive index model for estimating the permittivity of heterogeneous concrete models

Peer reviewedPublisher PD

Overview on nickel Carcinogenesis

Background: Acute exposure to nickel alters the pattern of gene expression in normal cells and induces a pattern of gene expression similar to that found in nickel-induced cancers. This study aims to review various mechanisms in nickel carcinogenesis. Materials and Methods: A systematic search on the Pubmed and Google scholar databases was done on the carcinogenic potency of nickel compounds in animal models and rodent cells in vitro. Results: Published evidence confirmed that the epigenetic activity of nickel carcinogenic compounds may be exerted with a modulation of gene expression. Nickel plays a role in the derivation of cells with neoplastic properties. Many researches demonstrated that nickel depletes intracellular ascorbate and may be able to replace the iron in the active site of hypoxia inducible factor-1a (HIF-1a) hydroxylases, which results in the inhibition of prolyl hydroxylase activity, activation of of hypoxia inducible factor-1a (HIF-1a), a protein known to be over-expressed in a variety of cancers and expression of hypoxia-inducible genes such as Cap43 gene. Cap43 gene was found to be highly inducible by hypoxia and over-expressed in cancer cells. These studies demonstrate that human exposure to Nickel turns on signaling for hypoxic stress, which may be important in its carcinogenesis. Conclusion: The major epigenetic effects of nickel are depletion of ascorbate, inhibition of prolyl hydroxylase enzyme activity, the stabilization of hypoxia inducible factor-1a (HIF-1a and expression of hypoxia-inducible genes such as Cap43 gene

The influence of defects on the mechanical properties of short fibre reinforced thermoplastics

SIGLEAvailable from British Library Document Supply Centre- DSC:DX92240 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

The difference in correlation between insulin resistance index and chronic inflammation in type 2 diabetes with and without metabolic syndrome

Background: Insulin resistance (IR) is associated with low-grade systemic inflammation. It plays an important role in the pathogenesis of type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD) in patients with metabolic syndrome (MetS). It is unclear whether diabetic patients with MetS confer elevated CVD risk and outcomes beyond the impact of individual's components of MetS. The aim of this study is to highlight the central role of IR, inflammation, triglyceride/high-density lipoprotein- cholesterol (TG/HDL-C) ratio, and atherogenic index of plasma (AIP) in T2DM with MetS. Materials and Methods: This cross-sectional study comprised 130 men distributed into three groups, namely Controls: 40 nondiabetic healthy volunteers; Group I: 40 T2DM patients without MetS, and Group II: 50 T2DM patients with MetS. Fasting blood samples were collected for the measurement of blood lipid profile, glucose, insulin, hemoglobin A1c, and high-sensitivity C-reactive protein (hs-CRP). TG/HDL-C ratio, AIP, and homeostasis model assessment of insulin resistance (HOMA-IR) were calculated. Results: Significant positive association was observed between HOMA-IR and hs-CRP only in Group II and between HOMA-IR and TG/HDL-C ratio in all subjects. Significant differences were seen in waist and hip circumferences, waist/hip ratio, body mass index, systolic blood pressure, fasting blood glucose, TGs, HDL-C, insulin, hs-CRP, HOMA-IR, TG/HDL ratio, and AIP between Controls and Group I with Group II. Conclusions: In T2DM with MetS, coexistence of elevated atherogenic indices, systemic inflammation, and association between HOMA-IR and TG/HDL-C ratio were seen. These factors are considered having important role in elevated CVD risk beyond MetS components in these patients

Preparing nanocomposite fibrous scaffolds of P3HB/nHA for bone tissue engineering

Nanocomposites are recently known to be among the most successful materials in biomedical applications. In this work we sought to fabricate fibrous scaffolds which can mimic the extra cellular matrix of cartilaginous connective tissue not only to a structural extent but with a mechanical and biological analogy. Poly(3-hydroxybutyrate) (P3HB) matrices were reinforced with 5, 10 and 15 %wt hydroxyapatite (HA) nanoparticles and electrospun into nanocomposite fibrous scaffolds. Mechanical properties of each case were compared with that of a P3HB scaffold produced in the same processing condition. Spectroscopic and morphological observations were used for detecting the interaction quality between the constituents. Nanoparticles rested deep within the fibers of 1 μm in diameter. Chemical interactions of hydrogen bonds linked the constituents through the interface. Maximum elastic modulus and mechanical strength was obtained with the presence of 5%wt hydroxyapatite nanoparticles. Above 10%wt, nanoparticles tended to agglomerate and caused the entity to lose its mechanical performance; however, viscoelasticity interfered at this concentration and lead to a delayed failure. In other words, higher elongation at break and a massive work of rupture was observed at 10%wt

Experimental investigation of the governing parameters in the electrospinning of poly(3-hydroxybutyrate) scaffolds : structural characteristics of the pores

We sought to determine the impact of electrospinning\ud parameters on a trustworthy criterion that\ud could evidently improve the maximum applicability of fibrous\ud scaffolds for tissue regeneration. We used an image\ud analysis technique to elucidate the web permeability index\ud (WPI) by modeling the formation of electrospun scaffolds.\ud Poly(3-hydroxybutyrate) (P3HB) scaffolds were fabricated\ud according to predetermined conditions of levels in a Taguchi\ud orthogonal design. The material parameters were the\ud polymer concentration, conductivity, and volatility of the\ud solution. The processing parameters were the applied voltage\ud and nozzle-to-collector distance. With a law to monitor\ud the WPI values when the polymer concentration or the\ud applied voltage was increased, the pore interconnectivity\ud was decreased. The quality of the jet instability altered the pore numbers, areas, and other structural characteristics, all of which determined the scaffold porosity and aperture interconnectivity. An initial drastic increase was observed in the WPI values because of the chain entanglement phenomenon above a 6 wt % P3HB content. Although the solution mixture significantly (p < 0.05) changed the scaffold architectural characteristics as a function of the solution viscosity and surface tension, it had a minor impact on the WPI values. The solution mixture gained the third place of significance, and the distance was approved as the least important factor

Scaffold percolative efficiency: in vitro evaluation of the structural criterion for electrospun mats

Fibrous scaffolds of engineered structures can be chosen as promising porous environments when an approved criterion validates their applicability for a specific medical purpose. For such biomaterials, this paper sought to investigate various structural characteristics in order to determine whether they are appropriate descriptors. A number of poly(3-hydroxybutyrate) scaffolds were electrospun; each of which possessed a distinguished architecture when their material and processing conditions were altered. Subsequent culture of mouse fibroblast cells (L929) was carried out to evaluate the cells viability on each scaffold after their attachment for 24 h and proliferation for 48 and 72 h. The scaffolds’ porosity, pores number, pores size and distribution were quantified and none could establish a relationship with the viability results. Virtual reconstruction of the mats introduced an authentic criterion, “Scaffold Percolative Efficiency” (SPE), with which the above descriptors were addressed collectively. It was hypothesized to be able to quantify the efficacy of fibrous scaffolds by considering the integration of porosity and interconnectivity of the pores. There was a correlation of 80% as a good agreement between the SPE values and the spectrophotometer absorbance of viable cells; a viability of more than 350% in comparison to that of the controls