Nanocomposites of Layered Clays and graphene/graphene oxide for drug delivery

Layered double hydroxides (LDH) comprise a class of materials that can be either found as natural minerals or can be synthetically prepared. Their structure is composed of a mixture of divalent and trivalent metal cations, forming brucite-like layers, that are neutralized with anions in the interlayer gallery. They have unique physical and chemical characteristics such as: high surface area, large charge density, biocompatibility and exchange capacity. These have attracted attention to the LDHs as potential drug delivery vehicles. Graphene (G) has also attracted the attention to exceptional properties, such as huge surface area, charge density concentration, membrane permeability by piercing mechanism and many others, expanding its use to include biomedical applications, such as drug delivery. Moreover, the possibility of large scale production of exfoliated graphene oxide (GO) sheets from G offered a further opportunity for their use. GO has a high exposed oxygenated surface that allows loading of large number of drugs by different bonding interactions and is dispersible in water. Alendronate sodium is a water soluble nitrogen containing bisphosphonate (nBP) drug, that has low bioavailabilty (\u3c 1 %) due to its low epithelial permeability. It also exhibits gastrointestinal adverse effects. The objective of the work is to create a hybrid nanocomposite of Zn-Al LDH in its nitrate form with G/GO, (G/GO-Zn-Al-NO3 LDH), combining the properties of these structures: membrane permeability and large interacting surface of G or GO, the buffering effect and the capability of the LDH in storing and controlling the drug release. The hybrid nanocomposites incorporated 2% w/w of G or GO with two different M2+/M3+ ratios of LDH, 2:1 and 3:1. They were loaded with the drug by co-precipitation and ion exchange. The samples were characterized by XRD, FTIR, Zetasizer analyzer, and the amount of drug loaded and released were determined by UV/Vis spectroscopy, and the results were compared to those of drug-LDH controls. Samples that have show successful intercalation of the drug in bi-layered arrangement are: co-precipitation samples using M2+/M3+ ratio of 3:1 (drug-LDH, G/GO-LDH), and ion-exchange samples, that don’t incorporate G/GO (drug-LDH), prepared using either M2+/M3+ ratios of 2:1or 3:1. Their loading amounts ranged from 25.4 to 51 % w/w, and they exhibited a sustained release over 24 hours with a release percentages, ranging from 2.1% (1.07 mg) up to 4.2 % (1.52 mg). The other samples showed loading by surface adsorption on brucite-like layers of the LDH and the G or GO. They have drug loading amounts ranging, from 12.4 to 57.3 % w/w. This work demonstrated the potential of G/GO-Zn-Al LDH nanocomposites for sustained drug delivery

Performance of Isolated Footing with Several Corrosion Levels under Axial Loading

This research aims to illustrate the corrosion process and its effect on the deterioration of reinforced concrete (RC) isolated footings using a small-scale model (1/8) and present the results of a prototype-scale study using a numerical model with different concrete depths and corrosion levels under axial load. The experimental program consisted of testing five small-scale (1/8) model RC isolated footings under axial loading after subjecting them to accelerated corrosion tests with a constant current. The main variable in the small-scale sample test was the corrosion level. This study presents an experimental approach, using the constant current method and the finite element method (FEM) with the ABAQUS package, to examine its effect on the axial load behavior under different corrosion ratios, which were 0%, 4.21%, 9.11%, 24.56%, and 30.67%. On the prototype scale, the variables were the corrosion level and the RC depths of 300 mm, 400 mm, and 500 mm. The results indicated that the average deviation in ultimate load between the experimental and FEM outcomes for the small-scale was below 5.6%, while the average deflection deviation was 6.8%. Also, the study found that an increase in the depth of the RC footing and corrosion ratio led to a more pronounced impact of the cracking pattern in the concrete and corroded bars, as well as a greater difference in the failure load. The experimental results suggest that the proposed numerical model is accurate and effective. These findings have important implications for the evaluation of isolated footings affected by corrosion damage using FEM, and can help inform decisions related to their design and maintenance. The failure loads of non-corroded footings with different depths were compared with the ECP-203 provisions of the 2018 Egyptian Code, and how corrosion ratios can be simulated by numerical models. The percentage variation between the design loads by code and the numerical loads by ABAQUS for controlled footings with thicknesses of 300, 400, and 500 mm was found to be 73%, 80%, and 78%, respectively. Using the derived relationship, the equivalent corrosion ratio percentages were 23.8%, 20.2%, and 32%, respectively. Doi: 10.28991/CEJ-2023-09-06-011 Full Text: PD

Investigating the factors of selecting audit clients: Evidence from an emerging market

This study investigates the insights and criteria audit partners use to select prospective clients in an emerging market. We use questionnaires to solicit responses from a sample of auditors at the partner/manager level in Big and non-Big 4 audit firms with international affiliations in an emerging economy. Descriptive statistical tools including the chi-square test and multiple logistic regression analysis are used for the analysis. This study finds that auditor reputation enhancement and corporate governance effectiveness are significantly associated with the acceptance of listed companies and that the higher financial reporting quality of listed companies and the need to promote audit and assurance services are significant factors affecting such decisions. Audit firms tend to select parents or subsidiaries because of the expected effective audits and reduced misstatement and litigation risks and audit firm industry expertise is needed to mitigate expected client risks to significantly affect the selection of clients with prior-year audit qualifications. Fraud is significantly associated with the selection of clients with prior violations reported by government monitoring bodies. This study is among the few empirical studies in emerging economies that provide insights from practicing auditors on a set of comprehensive attributes that affect the selection of audit clients. The findings have implications for audit partners and firms, auditees, and the audit profession in selecting clients that fit the firm’s and profession’s vision of audit branding and reputatio

Compression with Exact Error Distribution for Federated Learning

Compression schemes have been extensively used in Federated Learning (FL) to reduce the communication cost of distributed learning. While most approaches rely on a bounded variance assumption of the noise produced by the compressor, this paper investigates the use of compression and aggregation schemes that produce a specific error distribution, e.g., Gaussian or Laplace, on the aggregated data. We present and analyze different aggregation schemes based on layered quantizers achieving exact error distribution. We provide different methods to leverage the proposed compression schemes to obtain compression-for-free in differential privacy applications. Our general compression methods can recover and improve standard FL schemes with Gaussian perturbations such as Langevin dynamics and randomized smoothing

Medial sural artery perforator flap in reconstruction of soft tissue defect in upper and lower extremities: a clinical study

Background: The quality of soft tissue reconstruction in upper and lower extremities caused by trauma, infection, burns, and tumor resection affects the patient function and esthetic outcome. Many flaps have been described in the literature to reconstruct such defects. Medial sural artery perforator flap is one of the options for reconstruction of upper and lower extremities. Patients and methods: Starting from July 2019 through August 2020, 20 pedicled and free MSAP flaps were used for reconstruction of upper and lower limbs soft tissue defects. Results: total flap loss occurred in two cases, partial flap loss occurred in two cases and the flap was abandoned in two cases. Otherwise, all flaps survived well. Conclusion: MSAP flap is an excellent option in the reconstruction of soft tissue defects in upper and lower extremities

Simultaneous determination of Simvastatin and Sitagliptin in tablets by new univariate spectrophotometric and multivariate factor based methods

Five simple, sensitive and precise spectrophotometric and chemometric methods were used for simultaneous determination of Simvastatin (SM) and Sitagliptin (SIT) in their pure powdered forms and in the tablets. The proposed methods are the extended ratio subtraction method (EXRSM), ratio difference method (RDSM), mean centering of ratio spectra method (MCR) and chemometric methods, namely principal component regression (PCR) and partial least squares (PLS). In EXRSM; SM was determined at 237.5 nm, while SIT was determined at 267 nm, in RDSM; the difference in amplitudes at 237.5 and 245.5 nm was used for SM and 263.5 and 248.0 nm for SIT, while in MCR; SM and SIT were determined at 239.0 and 273.0 nm, respectively. PCR and PLS are factor based multivariate methods which utilize the whole spectra of SM and SIT. The developed methods were successfully applied for the determination of the studied drugs in their bulk powder, laboratory prepared mixtures and in tablets. All validation parameters of the developed methods were determined. The obtained results were statistically compared with each other along with a reported method

Comparative evaluation for an improved direct instantaneous torque control strategy of switched reluctance motor drives for electric vehicles

Due to the expected increase in the electric vehicles (EVs) sales and hence the increase of the price of rare-earth permanent magnets, the switched reluctance motors (SRMs) are gaining increasing research interest currently and in the future. The SRMs offer numerous advantages regarding their structure and converter topologies. However, they suffer from the high torque ripple and complex control algorithms. This paper presents an improved direct instantaneous torque control (DITC) strategy of SRMs for EVs. The improved DITC can fulfill the vehicle requirements. It involves a simple online torque estimator and a torque error compensator. The turn-on angle is defined analytically to achieve wide speed operation and maximum torque per ampere (MTPA) production. Moreover, the turn-off angles are optimized for minimum torque ripples and the highest efficiency. In addition, this paper provides a detailed comparison between the proposed DITC and the most applicable torque control techniques of SRMs for EVs, including indirect instantaneous torque control (IITC), using torque sharing function (TSF) strategy and average torque control (ATC). The results show the superior performance of the proposed DITC because it has the lowest torque ripples, the highest torque tor current ratio, and the best efficiency over the low and medium speed ranges. Moreover, the comparison shows the advantages of each control technique over the range of speed control. It provides a very clear overview to develop a universal control technique of SRM for EVs by merging two or more control techniques