Robust Synchronization of Ambient Vibration Time Histories Based on Phase Angle Compensations and Kernel Density Function

The output-only modal analysis is ubiquitously used for structural health monitoring of civil engineering systems. The measurements for such applications require the use of multiple data acquisition systems (DAS) to avoid complicated meshes of cables in high-rise buildings, avoid traffic constriction on a bridge during measurements, or to avoid having limited channels in a single DAS. Nevertheless, such requirements introduce time synchronization problems which potentially lead to erroneous structural dynamic characterization and hence misleading or inconclusive structural health monitoring results. This research aims at proposing a system-identification-based time synchronization algorithm for output-only modal analysis using multiple DAS. A new procedure based on the compensation of the phase angle shifts is proposed to identify and address the time synchronization issue in ambient vibration data measured through multiple DAS. To increase the robustness of the proposed algorithm to the inherent inconsistencies in these datasets, the kernel density function is applied to rank multiple time-shift estimates that are sometimes detected by the algorithm when inaccuracies exist in the data arising from low signal-to-noise ratio and/or presence of colored noise in the ambient excitations. First, the synchronized ambient vibration dataset of a full-scale bridge is artificially de-synchronized and used to present a proof of concept for the proposed algorithm. Next, the algorithm is applied to ambient vibration data of a 30-story, reinforced concrete building, where the synchronization of the data could not be achieved using two DAS despite best efforts. The application of the proposed time synchronization algorithm is shown to both detect and correct the time synchronization discrepancies in the output-only modal analysis

Experimental Investigations of a Single-Slope Solar Still: Energy and Exergy Analysis

Fresh water is one of the prime necessities of a society; however, its availability is becoming a major concern with the increasing population. There are not enough sources of fresh water at present due to the high rate of population increase. Many regions worldwide face limited access to fresh water. Given economic limitations, there is an urgent need to create and market technologies enabling households to generate their fresh water. In areas with abundant solar energy and proximity to seawater or well-water sources, solar still technology, if developed and commercialized, offers a cost-effective solution for freshwater needs. Thus, the current study is focused on exploring the potential of solar stills for producing fresh water. A single-slope solar still is designed, fabricated and experimentally tested for the production of fresh water. The results of the analysis indicate a maximum production of 2.88 L/day with an energy efficiency of 52.42% and an exergetic efficiency of 7.04%. Overall, the current study reveals significant potential in utilizing solar stills for producing fresh water, which could be increased further if research is conducted on modifying its basic design to increase its productivity

COST AND PERFORMANCE OPTIMIZATION OF PRECAST POST TENSIONED PRE-STRESSED GIRDER BRIDGE SUPERSTRUCTURES

Bridges are the most costly components of a road transportation network. Pre-stressed concrete girders with cast in place concrete decks are widely used for short to medium span bridges. The design and subsequent cost of a bridge depends on key geometric variables such as bridge width, number of lanes, number and length of spans, slab thickness, number and spacing of girders. Some of these variables are dictated by trafc demands and highway geometry, while others are related to structural demands. Typically, designing a bridge usually involves experience and expert judgement of the bridge engineer. This study is aimed at cost and performance optimization of pre-stressed concrete girder bridges using a parametric study of the design variables and their effects on cost and performance of the bridge. A spreadsheet is developed for analysis and design of deck slab and girders using one dimensional beam line analysis and AASHTO LRFD distribution factors. The spread sheet also calculates the overall cost of the bridge superstructure. This spreadsheet is then used to perform a parametric study by iterating through all design parameters. It is shown that, contrary to conventional wisdom, the cost and performance of bridge superstructure are not necessarily competing factors. Relationships for slab thickness and girder spacing are presented that result in optimal performance and cost of the bridge superstructure

Comparative Assessment of Phytoconstituents, Antioxidant Activity and Chemical Analysis of Different Parts of Milk Thistle Silybum marianum L.

Silybum marianum L. is a therapeutic plant belonging to the family Asteraceae, which has exhibited silymarin, a principal component used to cure various physiochemical disorders. The study appraised the phytochemical analysis, antioxidant activity and chemical analysis of an extract from the seed, stem and leaves. Qualitative and quantitative phytochemical analysis was evaluated by the Folin–Ciocalteu reagent method and aluminum chloride colorimetric method, respectively. While the antioxidant activity was determined by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and acetate buffer in ferric chloride (FRAP) assay, respectively, the chemical profile was evaluated by Gas Chromatography-Mass Spectrometry (GC-MS) assay. The study outcomes identified that alkaloids, glycosides, flavonoids, terpenoids, steroids and catcholic tannins were present in seed, stem and leaves extracts except for saponins and Gallic tannins. Whereas, phenols were absent only in seed extract. Quantitative analysis revealed the presence of phenols and flavonoids in appreciable amounts of 21.79 (GAE/g), 129.66 (QE/g) and 17.29 (GAE/g), 114.29 (QE/g) from the leaves and stem extract, respectively. Similarly, all extracts expressed reasonable DPPH inhibition (IC50) and FRAP reducing power such as 75.98, 72.39 and 63.21% and 46.60, 51.40 and 41.30 mmol/g from the seeds, stem and leaves extract, respectively. Additionally, chemical analysis revealed the existence of 6, 8 and 9 chemical compounds from the seeds, stem and leaves extract, respectively, corresponding to 99.95, 99.96 and 98.89% of the whole extract. The chemical compound, Dibutyl phthalate was reported from all extracts while, Hexadecanoic acid, methyl ester and Silane, (1,1-dimethylethyl), dimethyl (phenylmethoxy) were reported only from the seed and leaves extract. Moreover, Methyl stearate was also a major compound reported from all extracts except for seed extract. It is demonstrable that extracts from different parts of S. marianum possess significant antioxidant activity, as well as valuable chemical compounds accountable for therapeutic effects that might be incorporated as an alternative to synthetic chemical agents

Frequency and predictors of anxiety and depression among pregnant women attending tertiary healthcare institutes of Quetta City, Pakistan

Abstract Background Anxiety and depression (A&D) are commonly reported among pregnant women from all over the world; however, there is a paucity of workable data from the developing countries including Pakistan. The current study, therefore, aims to find out the frequency and predictors of A&D among pregnant women attending a tertiary healthcare institutes in the city of Quetta, in the Balochistan province, Pakistan. Methods A questionnaire based, cross-sectional survey was conducted. The pre-validated Hospital Anxiety and Depression Scale (HADS) were used to assess the frequency of A&D among study respondents. Anxiety and depression scores were calculated via standard scoring procedures while logistic regression was used to identify the predictors of A&D. SPSS v. 20 was used for data analysis and p < 0.05 was taken as significant. Results Seven hundred and fifty pregnant women responded to the survey. The majority of the respondents belonged to age group of 26–35 year (424, 56.4%) and had no formal education (283, 37.6%). Furthermore, 612 (81.4%) of the respondents were unemployed and had urban residencies (651, 86.6%). The mean anxiety score was 10.08 ± 2.52; the mean depression score was 9.51 ± 2.55 and the total HADS score was 19.23 ± 3.91 indicating moderate A&D among the current cohort. Logistic regression analysis reported significant goodness of fit (Chi square = 17.63, p = 0.030, DF = 3), indicating that the model was advisable. Among all variables, age had a significant association when compared with HADS scores [adjusted OR (odds ratios) = 1.23, 95% CI = 1.13–1.62, p < 0.001]. Conclusion Moderate A&D was reported among the study respondents. Furthermore, age was highlighted as a predictor of A&D. The evidence from this study provides a motion of support programs for anxious and depressed pregnant women. The benefits of implementing good mental health in antenatal care have long-lasting benefits for both mother and infant. Therefore, there is a need to incorporate A&D screening in the existing antenatal programs