Synthesis and characterisation of gel-derived mullite precursors from rice husk silica

The sol–gel synthesis and characterization of mullite precursor derived from rice husk silica and aluminum nitrate hydrate [(Al(NO₃)₃·9H₂O] has been investigated. The samples were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) coupled with Rietveld analysis, and scanning electron microscopy (SEM). FTIR results showed the presence of Si–O–Si, Al–O–Al, and Si–O–Al functional groups, which were associated with mullite, corundum, quartz, and cristobalite, as verified by XRD analysis. It is concluded that mullite formation started at 1150 °C, and its abundance increased rapidly with an increase in temperature from 1150 to 1350 °C, resulting in increased phase content from 30.9 to 67.7 wt%. Although mullite was formed at a low temperature, the complete reaction between corundum and silica to form mullite was not achieved. This finding demonstrated that rice husk silica is a potential alternative raw material for the production of mullite ceramic.     

Evaluation of chromogenic culture media for rapid identification of microorganisms isolated from cows with clinical and subclinical mastitis

This study aimed to evaluate the diagnostic performance (specificity, Sp; sensitivity, Se; accuracy; positive predictive value; negative predictive value; and Cohen's kappa coefficient, κ, of agreement) of chromogenic culture media for rapid identification of microorganisms isolated from cows with clinical (CM) and subclinical mastitis (SCM). For this, 2 experiments were carried out: evaluation of (1) biplate, and (2) triplate of chromogenic culture media for rapid identification of mastitis-causing microorganisms. For the evaluation of diagnostic performance, identification of microorganisms by MALDI-TOF mass spectrometry was considered the standard methodology. In experiment 1, 476 milk samples collected from cows with CM and 660 from cows with SCM were evaluated by inoculation in 2 selective chromogenic culture media (CHROMagar) for gram-positive bacteria and another for gram-negative bacteria. In experiment 2, 476 milk samples from cows with CM and 500 from cows with SCM were evaluated by inoculation in triplate chromogenic culture media (Smartcolor2, Onfarm), selective for Streptococcus and Strep-like organisms, Staphylococcus, and gram-negative bacteria. In experiment 1 for the CM samples, the use of biplates with gram-positive and gram-negative culture media showed Se that ranged from 0.56 (0.32–0.81; Staphylococcus aureus) to 0.90 (0.80–0.99 Streptococcus uberis), Sp varied from 0.94 (0.92–0.96; Strep. uberis) to 1.00 (Prototheca spp. or yeast), and κ ranged from 0.47 (0.26–0.67; Staph. aureus) to 0.84 (0.78–0.9; Escherichia coli). The Se of biplates for SCM samples ranged from 0.50 (0.15–0.85; E. coli) to 0.94 (0.87–1.00; Staph. aureus), Sp varied from 0.95 (0.93–0.97; Strep. uberis) to 0.99 (0.98–1.00; Staph. aureus and Strep. Agalactiae or dysgalactiae), and κ ranged from 0.18 (0.00–0.40; Escherichia coli) to 0.88 (0.80–0.95; Staph. aureus). In experiment 2, the Se of the triplate chromogenic media in CM samples ranged from 0.09 (0.00–0.26; Serratia spp.) to 0.94 (0.85–1.00; Klebsiella spp. and Enterobacter spp.), Sp varied from 0.94 (0.92–0.96; Strep. agalactiae and Strep. dysgalactiae) to 1.00 (Serratia spp.) and κ ranged from 0.07 (0.00–0.24; Serratia spp.) to 0.85 (0.75–0.94; Klebsiella spp. and Enterobacter spp.). For SCM samples, the use of the triplate with the chromogenic culture media showed Se that varied from 0.25 (0.10–0.40; Lactococcus spp.) to 1.00 (Strep. Agalactiae or dysgalactiae), Sp ranged from 0.92 (0.90–0.94; Strep. Agalactiae and Strep. dysgalactiae) to 0.99 (0.98–1.00; Klebsiella spp. and Enterobacter spp.), and κ varied from 0.28 (0.00–0.72; E. coli) to 0.72 (0.60–0.82; Staph. aureus). Our results suggest that the diagnostic accuracy of the biplate and triplate of chromogenic culture media varies according to pathogen, and the results of chromogenic culture media may be useful for rapid decision-making on mastitis treatment protocols of the main mastitis-causing microorganisms, but their use for implementation of mastitis control measures will depend on each farm specific needs.     

End-use energy utilization efficiency of Nigerian residential sector

In this paper, the end-use efficiencies of the different energy carriers and the overall energy efficiency in the Nigerian residential sector (NRS) were estimated using energy and exergy analysis. The energy and exergy flows were considered from 2006 to 2011. The overall energy efficiency ranges from 19.15% in 2006 to 20.19% in 2011 with a mean of (19.96±0.23)% while the overall exergy efficiency ranges from 4.34% in 2006 to 4.40% in 2011 with a mean of (4.31±0.059)%. The energy and exergy efficiency margin was 15.58% with a marginal improvement of 0.07% and 0.02%, respectively when compared with previous results. The contribution of the energy carriers to the total energy and exergy inputs were 1.45% and 1.43% for electricity, 1.95% and 3% for fossil fuel and 96.6% and 95.57% for bio-fuel. The result shows that approximately 65% of the residence use wood and biomass for domestic cooking and heating, and only a fraction of the residence have access to electricity. LPG was found to be the most efficient while kerosene, charcoal, wood and other biomass the least in this order. Electricity utilization exergy efficiency is affected by vapor-compression air conditioning application apart from low potential energy applications. In addition, this paper has suggested alternatives in the end-use application and has demonstrated the relevance of exergy analysis in enhancing sustainable energy policies and management and improved integration techniques.     

CFD evaluation of pressure drop across a 3-D filter housing for industrial gas turbine plants

This paper investigated the flow distribution and total pressure drop across a designed 3-D filter housing integrated with a 3-stage filtration system using computational fluid dynamics (CFD). The filter housing model was proposed for a heavy-duty industrial gas turbine plant operating at an average ambient temperature of 20°C.The pressure drops across the classes of filters were 652.8 Pa, 2692.2 Pa, 887.8 Pa, 776.2 Pa and 2304.2 Pa for I-GB, GB-GA, GA-FA, FA-HA, and HA-O, respectively. The results obtained indicated an acceptable total pressure drop of 7.2% for the entire filter housing before filter clean-up. Although the CFD simulation result shows that small outlet flow velocity and transonic flows exist at the outlet of the filter housing, the designed filter housing was proved compatible with the studied GT, for inlet flow conditions between 600≤W _air≤610 kg/s and 60≤v _air≤70 m/s for the air flow rate and velocity, respectively. Furthermore, the designed filter housing could be adopted for the studied GT and locations of Usan and Maiduguri in Nigeria, and other locations with similar environmental conditions.     

Effects of pulsed thermosonication treatment on fungal growth and bioactive compounds of Berberis vulgaris juice

In this study, the single and combined effects of pulsed‐ultrasound amplitude (100 W, 30 kHz with 25 and 50% amplitude levels for up to 30 min) and temperature (65 °C and 75 °C) on fungal growth, total phenolics, flavonoids and antioxidant activity of Berberis vulgaris juice were investigated. The combination of pulsed ultrasound at 50% amplitude for 30 min at temperature of 75 °C as the most effective treatment was resulted in a reduction of about?3.083 ± 0.02, ?3.04 ± 0.03, ?3.10 ± 0.01 and ?2.88 ± 0.02 log (N/N₀) on S. cerevisiae, A. flavus, A. versicolor and B. fulva, respectively. Additionally, the highest total phenolics, flavonoids and antioxidant activity were noted for the barberry juice after 30 min of sonication with 50% pulsed‐ultrasound amplitude at either 65 °C or 75 °C. Pulsed thermosonication is a promising technology to extend the shelf life of B. vulgaris fruit juice because of the improvement of antioxidant activity as well as microbial quality.     

From Metallurgical-Grade to Solar-Grade Silicon: An Overview

The non-renewable nature of fossil fuels as an energy source means its future availability is a cause for concern. The world’s energy demand is ever increasing and there is a growing interest in finding alternative renewable, environmentally benign and cheap energy sources like solar energy. This has resulted in the shortage of silicon feedstock for the photovoltaic industry. This is mainly due to the non-availability of a dedicated solar silicon production and the growing demand for silicon feedstock. There has been tremendous research in a quest to develop methods for the production of solar-grade silicon in a cheap and environmentally friendly way. The metallurgical and chemical routes for the production of solar-grade silicon from metallurgical-grade silicon have evolved. The chemical methods are the most researched ones and they are mostly preferred than the metallurgical ones since the former are capable of producing silicon of higher purity. This review discusses some of the available methods so far for the production of solar-grade silicon using metallurgical-grade silicon as a starting material.     

平面内疲劳荷载作用下带有钢管混凝土弦杆的方形中空截面T形节点的受力分析

近年来,钢管混凝土节点在桥梁工程中的应用越来越广泛。因此需要对这些节点在疲劳荷载作用下的可靠性进行研究,以避免可能突然发生的灾难。对由具有方形中空截面(SHS)的弦杆和支撑构成的中空截面T形节点进行了分析。具有中空截面的弦杆中填充了混凝土,因此形成了焊接组合管状T形节点。对此类节点进行的静力加载试验,校验了应变状态,以确定容易产生裂纹的热点区的应力集中系数。同时也对平面内弯曲循环荷载作用下的支撑的焊接组合节点进行了疲劳试验,以得到应力范围-循环次数(S-N)关系曲线的数据。在焊接的组合管状T形节点的热点区得到的应力集中系数最大值远远小于无任何填充的中空截面T形节点中的应力集中系数最大值。无论是弦杆还是支撑,其中的焊接组合管状T形节点中的疲劳破坏,都是在构件的焊趾处形成初始裂纹以及裂纹的发展过程中产生的。大量的试验也表明,破坏往往是先在弦杆的焊趾处产生第一道裂纹。研究同时发现,填充的焊接组合管状T形节点也比无填充的中空T形节点具有更好的抗疲劳强度。通过运用热点区应力方法进行的疲劳分析,提出了应用于填充混凝土弦杆的中空T形节点的设计方法。     

Plastic mechanism analysis of welded thin-walled T-joints made up of circular braces and square chords under in-plane bending

Welded thin-walled T-joints made up of circular hollow section (CHS) braces and square hollow section (SHS) chords were tested under static in-plane bending load. The hollow sections are cold-formed and have thicknesses less than 4 mm. The CHS-SHS T-joints are used in building the undercarriages and structural supports of equipment and structural systems used in the road transport and agricultural industries. Failure in the CHS-SHS T-joints was observed to occur as a result of chord-face yielding. Chord cracking was also observed after large deformations, resulting in a peak load being attained in these joints. There is no design formula in the existing CIDECT design guides, IIW static recommendation and Eurocode 3 for CHS-SHS T-joints under in-plane bending. In this paper, load versus chord flange indentation graphs, for the CHS-SHS T-joints are used to determine the deformation limit that defines the ultimate strength of the joints. The deformed shape of the chord observed from experimental tests is used to create a yield line model. The weld size and the rounded corners of the SHS chord are considered in the model. A formula is derived, for the ultimate strength of the CHS brace and SHS chord vierendeel connections based on a plastic mechanism analysis using yield line theory. There is a reasonably good agreement between the ultimate strength predicted using this formula and that determined experimentally.     

A collision-free formation reconfiguration control approach for Unmanned Aerial Vehicles

Formation flying of Unmanned Aerial Vehicles (UAVs) has gained a lot of interest due to its many potential advantages. Flying in formation allows wider sensing coverage area and in effect, this leads to improved surveillance and enhanced situational awareness. Also flying in formation eases coordination and data fusion. This paper presents the control architecture for fixed-wing UAV reconfiguration control using a novel combination of known techniques. The current premise is for the UAVs to assume their final target states within a specified time interval while avoiding collisions with one another or with an obstacle during the process. Some simulations are performed to assess the performance of the reconfiguration control scheme. The effects of the control parameters on the reconfiguration trajectories are also examined.