Investigation on the Mechanical, Microstructural, and Electrical Properties of Graphene Oxide-Cement Composite

Nanotechnology refers to the use of the materials or particles ranging from a few nanometers (nm) to 100 nanometers (nm) in a wide range of applications. Use of nanomaterials in cement composite to enhance the mechanical properties, fracture toughness and other functionalities has been studied for decades. In this regard, one of the carbon-based nanomaterials, Graphene Oxide (GO), has received attentions from researchers for its superior mechanical properties (e.g. tensile strength, yield strength, and Young\u27s modulus). Although GO is not lucrative in increasing electrical conductivity (EC) of cement paste compared to that of graphene- another derivative of GO, reduced graphene oxide (rGO), might be a solution to increase EC. Another derivative of GO is the solution to the problem. In this research, the compressive strength and flexural strength of GO-cement composite (GOCC) and rGO-cement composite (rGOCC) have been investigated with 0.01% and 0.05% GO and rGO content. GOCC-0.05% showed 27% increase in compressive strength compared to the control cement paste after 28 days (d) of hydration. GOCC-0.01% showed only 3.4% increase in compressive strength compared to the control. rGOCC-0.05% showed 21% increase in compressive strength and 15.5% increase in Modulus of Rupture (MOR) compared to the control cement paste after 28 d of hydration. On the other hand, rGOCC-0.01% showed 7% increase in compressive strength and 0.35% increase in MOR after 28 d. GOCC-0.05% showed increasing trends in compressive strength after 28 d indicating continuation of hydration. Similarly, rGOCC-0.05% also showed increasing trends in compressive and flexural strength after 28 d, possibly due to the reason described earlier. Microstructural investigation on GOCC-0.05% and GOCC-0.01% by X-ray Diffraction (XRD) illustrated that the crystallite sizes of tobermorite-Å and jennite, which are mineralogical counterpart of disordered Calcium-Silicate-Hydrate (C-S-H), increases from 3 d to 28 d, representing the crystallite growth due to continued hydration. However, the crystallite size of GOCC-0.05% was smaller than that of GOCC-0.01% at both 3 d and 28 d, indicating finer nucleated grains. According to Hall-Petch equation, mechanical strength increases with decreasing particle size. Finer particles or grains can increase the strength in cement composites in several other ways: (1) GO acted as heterogeneous nucleation sites because of reactive functional groups. Activation energy was decreased by these defects in the cement paste, and consequently, numerous nuclei of C-S-H. with high surface area were formed, (2) because of finer grains, cracks are forced to move along a tortuous path, which makes the structure difficult to fail, and strength increased consequently (3) Finer grains of GOCC-0.05% created compacted hydration products decreasing porosity which can indirectly increase the strength. The above reasons, separately or in conjunction, might increase the strength of GOCC-0.05% and proved that GO is responsible for increasing heterogeneous nucleation sites during cement hydration. Early age hydration (EAH) characteristics were investigated for rGOCC specimens with 0.1% and 0.5% rGO content. Scanning Electron Microscope (SEM), Energy Dispersive X-ray analysis (EDX), and X-ray Diffraction (XRD) were employed to study the EAH characteristics. SEM/EDX, and XRD analysis were performed after 15 min, 1 h, 3 h and 24 h of hydration. (EAH) study on rGOCC-0.1% showed that at 15 min hydration, numerous precipitates of, possibly, C-S-H formed along the grain boundary (GB) of unhydrated cement grains. This served as visual confirmation of Thomas and Scherer\u27s Boundary Nucleation and Growth (BNG) model that hydration of cement grains was initiated by the short burst of nucleation of C-S-H embryos along GB. EDX on rGOCC-0.1% and rGOCC-0.5% showed that Ca/Si ratio in C-S-H was ~2.0. This finding indicated that C-S-H structure in this study was concurrent with that of impure jennite. XRD analysis also evidently showed that jennite was present, possibly possessing a short range ordered (SRO) structure, referring to local crystalline structure in a very short area. After consulting Chen\u27s work, it would be appropriate to say that C-S-H found in this study resembled more as C-S-H (II), which is disordered jennite. It was also observed that as expected with cement with nanomaterials, with continuing hydration, pore spaces were filled with hydration products such as C-S-H, ettringite, CH, sulfoaluminates etc,. Lastly, Electrical resistivity (ER) testing on 9 sets of rGOCC specimens was conducted. The specimen includes 0.5%, 1%, 5% rGO content, and the control conditioned in both oven dry (OD) and saturated surface dry (SSD). ER increased with the increase of rGO content from 0.5% and 1% compared to that of the control. However, the ER of rGOCC-5% was significantly decreased, showing 93% reduction compared to the control, which can be interpreted as a threshold value for sensing applications to be explored. As expected, large reduction of ER value occurred on the specimens with the SSD condition. This reduction can be attributed to the ionic conduction though the pore solution of the composites. As the rGO content increased, so did the potential nucleation sites for hydration (as can be seen in SEM images), which might block the number of contact points among the rGO, resulting in low conduction and high resistivity. However, as rGO content increased to 5%, the contact areas/points increased to a degree that could trump the nucleation seeding sites, resulting in decreased ER. The ER measured with the rGOCC specimens was comparable to that of cement composites incorporating carbon fibers (CF), and steel fibers, but higher content of rGO are required to have a similar ER range of those fiber cement composites. This might be due to smaller sizes of rGO sheets and lower aspect ratio compared to other nanofibers causing drastic reduction of electron tunneling mechanism compared to other fibers

Supporting ultra poor people with rehabilitation and therapy among families of children with cerebral palsy in rural Bangladesh (SUPPORT CP) : Protocol of a randomised controlled trial

Introduction Poverty is a key contributor to delayed diagnosis and limited access to early intervention and rehabilitation for children with cerebral palsy (CP) in rural Bangladesh. 97% of families of children with CP live below the poverty line in Bangladesh. Therefore, in low-and middle-income countries (LMICs), efforts to improve outcomes for children with CP (including health-related quality of life, motor function, communication, and nutritional attainments) should also include measures to improve family economic and social capital. We propose a randomised controlled trial (RCT) to evaluate the effectiveness of an integrated microfinance/livelihood and community-based rehabilitation (IMCBR) program for ultra-poor families of children with CP in rural Bangladesh. Material and methods This will be a cluster RCT comparing three arms: (a) integrated microfinance/livelihood and community-based rehabilitation (IMCBR); (b) community-based rehabilitation (CBR) alone; and (c) care-as-usual (i.e. no intervention). Seven clusters will be recruited within each arm. Each cluster will consist of 10 child-caregiver dyads totalling 21 clusters with 210 dyads. Parents recruited in the IMCBR arm will take part in a microfinance/livelihood program and Parent Training Module (PTM), their children with CP will take part in a Goal Directed Training (GDT) program. The programs will be facilitated by specially trained Community Rehabilitation Officers. The CBR arm includes the same PTM and GDT interventions excluding the microfinance/livelihood program. The care-as-usual arm will be provided with information about early intervention and rehabilitation. The assessors will be blinded to group allocation. The duration of the intervention will be 12 months; outcomes will be measured at baseline, 6 months, 12 months, and 18 months. Conclusion This will be the first RCT of an integrated microfinance/livelihood and CBR program for children with CP in LMIC settings. Evidence from the study could transform approaches to improving wellbeing of children with CP and their ultra-poor families

Psychometric validation of the Bangla fear of COVID-19 Scale: confirmatory factor analysis and Rasch analysis

The recently developed Fear of COVID-19 Scale (FCV-19S) is a seven-item uni-dimensional scale that assesses the severity of fears of COVID-19. Given the rapid increase of COVID-19 cases in Bangladesh, we aimed to translate and validate the FCV-19S in Bangla. The forward-backward translation method was used to translate the English version of the questionnaire into Bangla. The reliability and validity properties of the Bangla FCV-19S were rigorously psychometrically evaluated (utilizing both confirmatory factor analysis and Rasch analysis) in relation to socio-demographic variables, national lockdown variables, and response to the Bangla Health Patient Questionnaire. The sample comprised 8550 Bangladeshi participants. The Cronbach α value for the Bangla FCV-19S was 0.871 indicating very good internal reliability. The results of the confirmatory factor analysis showed that the uni-dimensional factor structure of the FCV-19S fitted well with the data. The FCV-19S was significantly correlated with the nine-item Bangla Patient Health Questionnaire (PHQ-90) (r = 0.406,

Error-Resilient Techniques For Digital Image Transmission Over Wireless Channels

This dissertation studies issues related to image communication and proposes several improved joint source-channel coding methods for efficient image data transmission over noisy channel. However, the applicability of these techniques vary to certain extent and hence, these are encapsulated in the form of three independent chapters

ARTICLE IN PRESS YDSPR:775 JID:YDSPR AID:775 /FLA [m3SC+; v 1.78; Prn:12/10/2007; 11:15] P.1 (1-10) Digital Signal Processing •• • (••••) •••–•••

www.elsevier.com/locate/dsp Error-resilient transmission of quality-scalable images over wireless channel

Error-resilient transmission of resolution-scalable image and video over wireless channels

A new robust transmission strategy for scalable image and video is proposed. To protect the coded bit-stream according to the channel conditions, the proposed scheme exploits the progressive by resolution' structure of the scalable code-stream and takes into account the unequal importance as well as the effect of channel errors at different resolution levels towards reconstructing the source. A salient feature of the algorithm is its compatibility for multimedia applications requiring multi-resolution transmission to single or multiple clients. Results show that the proposed algorithm enables considerable gains in terms of subjective and objective image qualities over existing approaches.(1

Design and analysis of discrete wavelet transform (DWT) for image compression using VHDL

This paper presents the use of lectronic Design Automation (DA) for implementing the 2-D Discrete Wavelet Transform (DWT) with P G2000 standard for image compression using Aldec Active HD. tool. The design flow starts with specifications of the system behavior for implementation on silicon and it ta es several steps before hardware implementation to meet the specifications. The software allows the analysis to ensure the designed chip satisfy the re uired specifications