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991.
Ahmet Çavdar 《Composites Part B》2012,43(5):2452-2463
The flexural strength and ductility properties of cementitious composites (mortar) under high temperature may be significantly improved by incorporating different types of fibers. In this study, four different types of fibers are added to cement mortars with the aim to investigate their mechanical contributions to mortars under high temperature, comparatively. Polypropylene (PP), carbon (CF), glass (GF) and polyvinyl alcohol (PVA) fibers are chosen for research. These fibers are added into mortars in five different ratios (0.0%, 0.5%, 1.0%, 1.50% and 2.0%) by volume. The mortars are subjected to the following temperatures: 21 °C (normal conditions), 100 °C (oven dry), 450 °C and 650 °C. The mechanical properties investigated are flexural strength, deflection and compressive strength of the cement mortars. In addition, thin sections of mortars are investigated to obtain changes in mortar because of high temperature. It is concluded that all fiber types contribute to the flexural strengths of mortars under high temperature. However, this contribution decreases with an increase in temperature. The samples with PVA show the best flexural performance (75–150%) under high temperature. CF which does not melt under high temperature also gives high flexural strength (11–85%). The compressive strengths of the mortars reduce under high temperature or with fiber addition. The highest increase in flexural strength and the lowest decrease in compressive strength is at 0.5–1.5% for CF if all temperature conditions are taken into consideration. The optimum fiber addition ratios of the samples containing PP and GF are 0.5% by volume. And for PVA, it is between 0.5% and 1.5% by volume. 相似文献
992.
Olives were collected from various districts of Turkey (North and South Aegean sub-region, Bursa-Akhisar, South East Anatolia
region) harvested over seven (2001–2007) seasons. The aim of this study was to characterize the chemical profiles of the oils
derived from single variety Turkish olives including Ayvalik, Memecik, Gemlik, Erkence, Nizip Yaglik and Uslu. The olive oils
were extracted by super press and three phase centrifugation from early harvest olives. Chosen quality indices included free
fatty acid content (FFA), peroxide value (PV) and spectrophotometric characteristics in the ultraviolet (UV) region. According
to the FFA results, 46% (11 out of 24 samples) were classified as extra virgin olive oils; whereas using the results of PV
and UV, over 83% (over 19 of the 24 samples) had the extra virgin olive oil classification. Other measured parameters included
oil stability (oxidative stability, chlorophyll pigment, pheophytin-α), cis–trans fatty acid composition and color index. Oxidative stability among oils differed whereas the cis–trans fatty acid values were within the national and international averages. Through the application of two multivariate statistical
methods, Principal component and hierarchical analyses, early harvest virgin olive oil samples were classified according to
the geographical locations categorized in terms of fatty acid profiles. Such statistical clustering gave rise to defined groups.
These data provide evidence of the variation in virgin olive oil quality, especially early harvest and cis–trans isomers of fatty acid profiles from the diverse agronomic conditions in the olive growing regions of Turkey. 相似文献
993.
Methanol oxidation on the aluminum-copper-silicon alloys which are coated with polyprrole were investigated in 1 N H2SO4 by using electrochemical method. For this purpose, first the current densitypotential curve of alloys were obtained in 1
N H2SO4 + x M pyrrole solutions, determined passive zones are coated with polyprrole alloys in H2SO4 solutions. Then the current-potential curves were obtained in 1 N H2SO4 + x M methanol with aluminum alloys and these are expected at +1.5 V against to the standard calomel electrode (SCE) at the different
times in 1 N H2SO4 + 10−3 M pyrrole that were obtained with different scan rates. The extreme methanol oxidation was seen on the E110 and E140 alloys
which are coated with polyprrole. Embedded pH electrode solutions which were coated with polypyrrole in 1 N H2SO4 and 1 N H2SO4 + 0.5 M methanol solutions were measured after 30 minutes at +2.1 V. 相似文献
994.
Compositions, antioxidant and antimicrobial activities of Helichrysum (Asteraceae) species collected from Turkey 总被引:1,自引:0,他引:1
The methanolic extracts of 16 Helichrysum species were investigated for their in vitro antioxidant, radical scavenging and antimicrobial activities. All the extracts showed strong antioxidant and radical scavenging activity. The highest total antioxidant capacity as ascorbic acid equivalents (AAE) of 194.64 mg/g dry extract was obtained for Helichrysum noeanum in the phosphomolybdenum assay. The highest IC50 value (7.95 μg/ml) was observed for the extract of Helichrysum stoechas subsp. barellieri in the DPPH assay. The total phenolic contents of the extracts ranged from 66.74 to 160.63 mg gallic acid equivalents (GAE)/g dry extract. The major component present in the extracts was identified as chlorogenic acid followed by apigenin-7-glucoside and apigenin by HPLC analysis. All the extracts showed significant antimicrobial activity against microorganisms containing 13 bacteria and two yeasts in the agar diffusion method. 相似文献
995.
The aim of this study was to investigate the incidence of Arcobacter species in water sources and raw milk from healthy animals in Kayseri, Turkey. A total of 175 samples of drinking water (n = 100), spring water (n = 25), and raw milk (n = 50) were examined. Arcobacter species were isolated using the membrane filtration technique. Overall, 7 (4%) of the 175 samples yielded Arcobacter spp.: 3 (3%) drinking water samples, 1 (4%) spring water sample, and 3 (6%) raw milk samples. Two species of Arcobacter were recovered from the seven positive samples: Arcobacter butzleri, Arcobacter skirrowii, and A. butzleri plus A. skirrowii found in 3 (1.7%), 2 (1.1%), and 2 (1.1%) samples, respectively. Our study is the first to report the isolation of both A. butzleri and A. skirrowii together from drinking water and is the first report of Arcobacter in milk from healthy cows in Turkey. Based on these findings, the presence of Arcobacter species in environmental waters and raw milk may pose a potential hazard for human health. 相似文献
996.
In Rhizopus oryzae cultivations, lactate production decreased and ethanol and biomass productions increased as inoculated spore concentration increased. Spore concentrations of 1 x 10(3) and 1 x 10(4) spores ml(-1) induced tightly packed clumps, whereas 1 x 10(5) and 1 x 10(6) spores ml(-1) induced filamentous growth. 相似文献
997.
Autonomic cardiovascular control following transient arousal from sleep: a time-varying closed-loop model 总被引:4,自引:0,他引:4
Blasi A Jo JA Valladares E Juarez R Baydur A Khoo MC 《IEEE transactions on bio-medical engineering》2006,53(1):74-82
Recent studies suggest that exposure to repetitive episodes of hypoxia and transient arousal can lead to increased risk for cardiovascular disease in patients with obstructive sleep apnea syndrome (OSAS). To obtain an improved understanding of and to quantitatively characterize the autonomic effects of arousal from sleep, a time-varying closed-loop model was used to determine the interrelationships among respiration, heart rate and blood pressure in 8 normal adults. A recursive least squares algorithm was used in combination with the Laguerre expansion technique to estimate the time-varying impulse responses of the 4 model components. We found that during arousal: 1) respiratory-cardiac coupling gain increases in nonrapid-eye movement (NREM) but not in REM sleep; 2) in both NREM and REM sleep, baroreflex gain shows an initial increase, but this is followed by a more sustained decrease below pre-arousal baseline levels, allowing sympathetic tone to be elevated over a relatively long duration; 3) the gains of other model components show increases with arousal that are consistent with the increased sympathetic modulation of systemic vascular resistance and contractility of the heart. These findings establish a normative database against which further measurements of cardiovascular arousal responses in OSAS may be compared. 相似文献
998.
İ. Çobanoğlu Ş. Bozdağ H. Kumsar 《Bulletin of Engineering Geology and the Environment》2008,67(3):367-374
The 1998 Ceyhan (Adana, Turkey) earthquake caused major damage to construction on caliche formations. Caliche (a heterogenous
secondary calcium carbonate deposit formed in arid and semi-arid regions) is widespread in the Adana area. The paper distinguishes
three types of caliche: massive, containing vegetation remains and containing gravel. The porosity, water absorption and unconfined
compressive strength of these three groups of caliche were determined. The compressive strengths are low compared to caliches
in other areas—an important consideration as Adana is the fourth largest city in Turkey.
相似文献
999.
Duygu Ağaoğulları Hasan Gökçe İsmail Duman M. Lütfi Öveçoğlu 《Journal of the European Ceramic Society》2012,32(7):1457-1462
In this study, AlB2 powders were synthesized by using a combined method of mechanical alloying (MA) and annealing of elemental aluminum (Al) and boron (B) powders. Milling was performed in a planetary ball-mill (Fritsch? Pulverisette 7 Premium Line) up to 15 h under argon (Ar) atmosphere. Annealing process was carried out in a tube furnace at 650 °C for 6 h under Ar atmosphere. The effects of MA durations on the annealing process and AlB2 formation were investigated. The conversion of Al and B powders to AlB2 starts after only MA for 3 h or after MA for 1 h and subsequent annealing. A slight formation of AlB12 occurs at 242 °C for as-blended powders and it shifts to about 272 °C for MA’d powders. Al–B powder blends MA’d for 9 h and annealed have AlB2 particles in size between 35 and 75 nm in the presence of Al13Fe4, Fe3B and Fe2B contaminations. 相似文献
1000.
Ahmet Kagz Zehra
zba Hasine Kagz Ismail Aydin 《Journal of the European Ceramic Society》2005,25(16):3547-3552
In the present work, machinable green gel-cast alumina compacts were prepared by using polyethyleneglycol (400) diacrylate (P4) and polyethyleneglycol (600) dimethacrylate (P6) together with the acrylamide (AAm) comonomer. The glass transition temperatures of copolymers decreased with the increasing of P4 or P6 amount in total copolymer. The green samples obtained in an aqueous system were mechanically analyzed by means of three-point bending. Flexural strength values increased, from 2 MPa to 25 MPa, as the weight ratio of P4 or P6 in total copolymer (AAm-P4 or AAm-P6) decreased from 90% to 3.5%, respectively. The green gel-cast samples prepared by using P4 or P6 were machined easily by using a lathe, drill and milling machine without damaging the samples, which have good surface finish. The binder removal was achieved at lower temperatures than those samples prepared by using only AAm. 相似文献