Influence of acid treatment and carbonation on the properties of recycled concrete aggregate

Recycled concrete aggregate (RCA), obtained by crushing of original (old) concrete, consists of natural aggregate grains and a cement mortar matrix. The presence of old adhered cement mortar, which has higher porosity than natural aggregate, causes unfavourable properties of RCA. The research conducted in order to improve the quality of RCA and to enable its greater application in the construction industry is presented in this paper. Therefore, RCA was subjected to quality improvement treatments with hydrochloric acid and carbon dioxide (accelerated carbonation). The first procedure was aimed at partially removing the adhered cement mortar and the second at reinforcing the cement matrix. The physical, mechanical and chemical properties of all three types of RCA were tested. After the pre-soaking acid treatment (0.1 mol/dm(3) HCl), RCA showed reduced water absorption (up to 3%); the process of accelerated carbonation also led to reduced water absorption (13-20%) as well as to improved mechanical properties (similar to 10%). A scanning electron microscopy investigation revealed that the carbonation process, as expected, significantly reduces porosity of RCA. The overall results show that if RCA is obtained by crushing of compact, high-quality concrete, the procedures of aggregate quality improvement are not necessary

The investigation of the presence of Clostridium botulinum spores in honey in Serbia

The presence of Clostridium botulinum spores in 59 honey samples originating from different regions of the Republic of Serbia was studied. In addition to microbiological methods, after enrichment, centrifugation and membrane filtration, molecular methods (PCR methods) were utilized. The number of spores in PCR positive samples was estimated by the most probable number (MPN) method. PCR confirmed C. botulinum spores in 5 (8.47%) honey samples. MPN of spores varied from 20/kg to 204/kg honey. PCR was more sensitive than cultural methods. Natural honey contamination with C. botulinum spores is low-level and not homogeneous, and therefore, PCR methods require multiple sub-sampling

Commercial P-Channel Power VDMOSFET as X-ray Dosimeter

The possibility of using commercial p-channel power vertical double-diffused metal-oxide-semiconductor field-effect transistors (VDMOSFETs) as X-ray sensors is investigated in this case study. In this aspect, the dependence of sensitivity on both the gate voltage and the mean energy for three X-ray beams is examined. The eight gate voltages from 0 to 21 V are applied, and the dependence of the sensitivity on the gate voltage is well fitted using the proposed equation. Regarding X-ray energy, the sensitivity first increases and then decreases as a consequence of the behavior of the mass energy-absorption coefficients and is the largest for RQR8 beam. As the mass energy-absorption coefficients of SiO2 are not found in the literature, the mass energy-absorption coefficients of silicon are used. The behavior of irradiated transistors during annealing at room temperature without gate polarization is also considered

Spectral reflectance indices as a phenotyping tool for assessing morpho-physiological traits of winter wheat (Triticum aestivum L.)

Morpho-physiological traits of wheat such as a grain weight per plant, total leaf chlorophyll content, carotenoids, relative dry matter and nitrogen content are important traits for the growth of winter wheat genotypes. However, methods to estimate these traits are laborious and destructive. Spectral reflectance indices based on combination of visible and near-infrared wavelengths such as NDVI (Normalized Difference Vegetation Index), represent one of the most promising tools for application in field phenotyping with potential to provide complex information on different morpho-physiological traits of wheat. The aim of this study was to assess the utility of NDVI measurements of wheat canopy in identification of a specific growth stage in which remotely sensed data show the largest correlation with final grain yield, grain weight per plant, total leaf chlorophyll and carotenoid content, relative dry matter and nitrogen content in 29 winter wheat (Triticum aestivum L.) genotypes. The NDVI was measured using an active hand-held sensor GreenSeeker (NTech Industries Inc., Ukiah, California, USA) and hyperspectral camera (Ximea Corp., Lakewood, CO USA) at four growth stages of wheat: full flowering (BBCH 65), medium milk (BBCH 75), early dough (BBCH 83) and fully ripe stage (BBCH 89). Overall 66 different hyperspectral NDVIs were calculated from two-band combinations between red (600-700 nm) or far red (700-740 nm) and near-infrared (756-946 nm) regions. Pearson’s correlation coefficient was used to explore the relationship among examined traits and NDVI measured at different growth stages of wheat. Obtained results indicate that most of observed NDVI indices showed negative correlation with the relative dry matter content at all observed growth stages. Significant positive correlations (higher than 0.6 and significant at P < 0.05) were found between the specific hyperspectral NDVIs measured at medium milk stage and grain weight per plant, total leaf chlorophyll, carotenoid and nitrogen content, as well as with final grain yield of wheat. The strong positive relationship between NDVI and examined traits found at medium milk stage suggests that this stage is the most appropriate for estimation of these traits of winter wheat in semiarid or similar wheat growing conditions. The overall results indicate that spectral reflectance tools based on combined visible and near-infrared wavelengths, such as NDVI, could be successfully applied to assess morpho-physiological traits of a large number of winter wheat genotypes in a rapid and non-destructive manner. Furthermore, although neither device appeared to have a sizeable advantage over the other, NDVI acquired by hyperspectral camera does appear to be more indicative than NDVI acquired by GreenSeeker sensor, suggesting that alternative spectral combinations can be used in assessing targeted traits of winter wheat genotypes. Abstract boo

Determining fracture mechanics parameters using the digital image correlation method on cylindrical samples produced by different additive manufacturing techniques

This work presents the difference in the values of fracture mechanics parameters obtained by testing of cylindrical specimens with a sharp notch, cut on the tip of a wider groove. The samples were obtained using two different additive manufacturing techniques. The first type of samples was obtained by the FDM (Fused Deposition Modeling) method, on the German REPRAP X400 device with an average accuracy of 0.25 mm. The second type of samples was made using the SLS (Selective Laser Sintering) method on the EOS Formiga P100 device with a production precision of 0.08 mm. Regardless of the difference in manufacturing techniques, the direction and orientation of the samples was identical. The samples were prepared so that during loading the fibers are loaded in tension, i.e. axially. Different lengths of the sharp notches were fabricated axially on the samples. The values of fracture mechanics parameters such as CMOD (Crack Mouth Opening Displacement) and CTOD-5 (Crack Tip Opening Displacement obtained using the -5 technique) were obtained using the digital image correlation method. The obtained parameters, except for mutual correlation, were also used for the verification of numerical results. In the future work, a procedure for determination of energy-based fracture mechanics parameters will be developed for this sample geometry

Statistička analiza rezultata ispitivanja fizičko-mehaničkih svojstava kontrolnih betonskih kocki

Cilj ovog istraživanja je prikupljanje, obrada i statistička analiza rezultata ispitivanja uzoraka betonskih kocki koji su ispitani u Laboratoriji za materijale Građevinskog fakulteta u Beogradu prema standardu SRPS ISO 4012:2000 u periodu od 2012. do 2017. godine. Za potrebe analize, preuzeti su podaci iz Izveštaja o ispitivanju kontrolnih betonskih kocki, prepoznate su i klasifikovane osnovne karakteristike očvrslog betona. Izvršena je statistička analiza datuma betoniranja, starosti uzoraka, sastava betona, zapreminske mase, čvrstoće pri pritisku, zahtevane marke betona itd. Statistika je pokazala da su najčešće upotrebljavani cementi sledećih oznaka: CEM II A-M (V-L), CEM II A-M (S-L), CEM II A-S, a da najveće učešće imaju marke betona MB 30 sa 66,8% i MB 40 sa 14,3% udela

Source Code Analysis in Programming Education: Evaluating Learning Content with Self-Organizing Maps

Due to the everchanging and evergrowing nature of programming technologies, the gap between the programming industry’s needs and the educational capabilities of both formal and informal educational environments has never been wider. However, the need to learn computer programming has never been greater, regardless of the motivation behind it. The number of programming concepts to be taught is increasing over time, while the amount of time available for education and training usually remains the same. The objective of this research was to analyze the source codes used in many educational systems to teach fundamental programming concepts to learners, regardless of their prior experience in programming. A total of 25 repositories containing 3882 Python modules were collected for the analysis. Through self-organization of the collected content, we obtained very compelling results about code structure, distribution, and differences. Based on those results, we concluded that Self-Organizing Maps are a powerful tool for both content and knowledge management, because they can highlight problems in the curriculum’s density as well as transparently indicate which programming concepts it has successfully observed and learned to recognize. Based on the level of transparency exhibited by Self-Organizing Maps, it is safe to say that they could be used in future research to enhance both human and machine learning of computer programming. By achieving this level of transparency, such an Artificial Intelligence system would be able to assist in overall computer programming education by communicating what should be taught, what needs to be learned, and what is known

Influence of acid treatment and carbonation on the properties of recycled concrete aggregate

Recycled concrete aggregate (RCA), obtained by crushing of original (old) concrete, consists of natural aggregate grains and a cement mortar matrix. The presence of old adhered cement mortar, which has higher porosity than natural aggregate, causes unfavourable properties of RCA. The research conducted in order to improve the quality of RCA and to enable its greater application in the construction industry is presented in this paper. Therefore, RCA was subjected to quality improvement treatments with hydrochloric acid and carbon dioxide (accelerated carbonation). The first procedure was aimed at partially removing the adhered cement mortar and the second at reinforcing the cement matrix. The physical, mechanical and chemical properties of all three types of RCA were tested. After the pre-soaking acid treatment (0.1 mol/dm3 HCl), RCA showed reduced water absorption (up to 3%); the process of accelerated carbonation also led to reduced water absorption (13–20%) as well as to improved mechanical properties (∼10%). A scanning electron microscopy investigation revealed that the carbonation process, as expected, significantly reduces porosity of RCA. The overall results show that if RCA is obtained by crushing of compact, high- -quality concrete, the procedures of aggregate quality improvement are not necessary

Part XVI - Stereospecific ligands and their complexes: Synthesis, characterization and In Vitro antiproliferative activity of new platinum(iv) complexes with some O,O'-dialkyl esters of (S,S)-ethylenediamine-N,N'-di-2-propanoic acid against breast cancer (MDA-MB-231) and colon cancer (HCT-116 and SW-480) cell lines

Synthesis of four new platinum(IV) complexes (C1-C4) with bidentate N,N'-ligand precursors, O,O'-dialkyl esters (L1-L4) (alkyl = ethyl, propyl, butyl and pentyl) of (S,S)-ethylenediamine-N,N'-di-2-propanoic acid, H2-S,S-eddp were reported. The platinum(IV) complexes were characterized by elemental analysis and their structures determined on the basis of infra-red, 1H and 13C NMR spectroscopy. Cyto-toxicity against human breast carcinoma MDA-MB-231, human colon carcinoma HCT-116 and SW-480 tumour cell lines was determined using the MTT assay, which indicated the larger the size of the complex or ligand, the greater the cytotoxicity