Study of the H + O + M reaction forming OH: Kinetics of OH chemiluminescence in hydrogen combustion systems

The temporal variation of OH^∗ (A²Σ⁺) chemiluminescence in hydrogen oxidation chemistry has been studied in a shock tube behind reflected shock waves at temperatures of 1400-3300 K and at a pressure of 1 bar. The aim of the present work is to obtain a validated reaction scheme to describe OH^∗ formation in the H₂/O₂ system. Temporal OH^∗ emission profiles and ignition delay times for lean and stoichiometric H₂/O₂ mixtures diluted in 97-98% argon were obtained from the shock-tube experiments. Based on a literature review for the hydrogen combustion system, the key reaction considered was H + O + M = OH^∗ + M (R1). The temperature dependence of the measured peak OH^∗ emission from the shock tube and the peak OH^∗ concentration from a homogeneous closed reactor model are compared. Based on these results a reaction rate coefficient of k₁ = (1.5 ± 0.4) × 10¹³ exp(−25 kJ mol⁻¹/RT) cm⁶ mol⁻² s⁻¹ was found for the forward reaction (R1) which is slightly higher than the rate coefficient suggested by Hidaka et al. (1982). The comparison of measured and simulated absolute concentrations shows good agreement. Additionally, a one-dimensional laminar premixed low-pressure flame calculation was performed for where absolute OH^∗ concentration measurements have been reported by Smith et al. (2005). The absolute peak OH^∗ concentration is fairly well reproduced if the above mentioned rate coefficient is used in the simulation.     

Fabrication of Mullite and Mullite-Matrix Composites by Transient Viscous Sintering of Composite Powders

Mullite was fabricated by a process referred to as transient viscous sintering (TVS). Composite particles which consisted of inner cores of α-alumina and outer coatings of amorphous silica were used. Powder compacts prepared with these particles were viscously sintered to almost full density at relatively low temperatures (∼1300°C). Compacts were subsequently converted to dense, fine-grained mullite at higher temperatures (∼1500°C) by reaction between the alumina and silica. The TVS process was also used to fabricate mullite/zirconia/alumina, mullite/silicon carbide particle, and mullite/silicon carbide whisker composites. Densification was enhanced compared with other recent studies of sintering of mullite-based composites. This was attributed to three factors: viscous flow of the amorphous silica coating on the particles, avoidance of mullite formation until higher temperatures, and increased threshold concentration for the development of percolation networks.     

Synthesis of Calix[4]arene-Based Thiourea Derivatives for Extraction of Toxic Dichromate and Arsenate Ions

In the environment, the presence of toxic oxyanions such as Cr(VI) and As(V), especially in drinking water, creates serious hazards to human health. For efficient and selective detection of these species; novel calix[4]arene-based thiourea derivatives which obtained using p-tert-butylcalix[4]arene as starting material have been prepared from m-aniline or o-aniline or o-aminophenol in moderate yield. The structures of all new synthesized compounds obtained from these reactions were determined by using FTIR, ¹H, and ¹³C NMR spectroscopy. The complexing properties of calix[4]arene-based thiourea derivatives have been studied towards the As(V) and Cr(VI). It was found that calix[4]arene-based thiourea derivative 5,11,17,23-tetra-tert-butyl-25,27-bis(o-amino-phenylthioureido propoxy)-26,28-hydroxycalix[4]arene is an effective extractant for carrying HCr₂O₇^2? anions.     

Colour and textural attributes of sucuk during ripening

The sensory (flavour, colour, and ease of cutting scores), colour (Hunter L, a, b, YI, total colour difference, hue angle, chroma, and browning index values) and textural (hardness, adhesiveness, springiness, cohesiveness, gumminess, chewiness, and resilience) attributes of sucuk were followed during the ripening period. Colour scores increased (P<0.05) from score 4 to 6 during the first 3 days of the ripening period and then decreased (P<0.05). The lightness (L values), yellowness (b), and hue angle of sucuk decreased (P<0.05) during the ripening period. The major colour changes occurred between the 5th and 9th days of the ripening period. Pearson correlation test indicates that a positive relationship (P<0.01) exists between a-values and sensory colour scores. The overall sensory scores changed (P<0.05) in parallel to the flavour scores. Hardness, gumminess, and chewiness of sucuk increased (P<0.05) during the ripening period. Strong relationships (P<0.01) were found between hardness and cutting scores. Adhesiveness values of sucuk decreased significantly (P<0.05) about 10 times from -9.3 to -92.6 during the ripening period. Springiness and cohesiveness values decreased during the ripening period, but not significantly (P>0.05). Cutting scores were related (P<0.01) to gumminess (0.921) and chewiness (0.922) values but not to resilience (P>0.05). It was observed that most instrumental colour and textural attributes were in agreement with sensory attributes. These results indicated that instrumental methods could be easily adapted and can be used for evaluation of quality attributes of sucuk during the ripening period.     

The optimum performance of a solar-assisted combined absorption–vapor compression system for air conditioning and space heating

The technique of energetic optimization is employed to investigate the optimal performance of an irreversible hybrid air-conditioning/heat pumping system consisting of a vapor compression refrigerator cascaded with a solar-driven absorption refrigerator. To get closer to a real system, the effect of internal irreversibilities on the performance of the hybrid system is considered. The optimal operating temperature of the solar collector and the maximum overall coefficient of performance (COP) of the cooling and heating modes of the system are derived. The results obtained here have more realistic meaning than those of reversible thermodynamics for the optimal design and operation of practical solar-driven hybrid systems.     

A multiline model for time-efficient estimation of crosstalk

This work proposes a novel and accurate crosstalk noise estimation method in the presence of multiple RC lines for use in design automation tools. Using the realistic exponential waveform and a reduced transfer function, the proposed model presents a complete multiline noise model by representing active and passive aggressors simultaneously on the victim line. In the model, active aggressors are easily represented by current sources and passive aggressors are accurately modeled as equivalent capacitances to victim. Each current source representing an active aggressor carries the same accuracy as the 2-π representation. Equivalent capacitances for passive aggressors, on the other hand, consider resistive shielding effect and the realistic exponential aggressor waveform. This approach allows one to obtain a general noise model that considers the effect of many active and passive aggressors and general formulas derived can easily be applied to real cases. Noise peak and width expressions are derived and results are in good agreement with HSPICE results. Results show that average error for noise peak is 4.3% and for the width is 6.9% while allowing for very fast analysis.     

The daily performance of a solar pond integrated with solar collectors

The present study deals with heat storage performance investigation of integrated solar pond and collector system. In the experimental work, a cylindrical solar pond system (CSPS) with a radius of 0.80 m and a depth of 2.0 m and four flat plate collectors dimensions of 1.90 m × 0.90 m was built in Cukurova University in Adana, Turkey. The CSPS was filled with salty water of various densities to form three salty water zones (Upper Convective Zone, Non-Convective Zone and Heat Storage Zone). Heat energy collected by collectors was transferred to the solar pond storage zone by using a heat exchanger system which is connected to the solar collectors. Several temperature sensors connected to a data acquisition system were placed vertically inside the CSPS and at the inlet and outlet of the heat exchanger. Experimental studies were performed using 1, 2, 3 and 4 collectors integrated with the CSPS under approximately the same condition. The integrated solar pond efficiencies were calculated experimentally and theoretically according to the number of collectors. As a result, the experimental efficiencies are found to be 21.30%, 23.60%, 24.28% and 26.52%; the theoretical efficiencies to be 23.42%, 25.48%, 26.55% and 27.70% for 1, 2, 3 and 4 collectors, respectively. Theoretical efficiencies were compared with the experimental results and hence a good agreement is found between experimental and theoretical efficiency profiles.     

Neither oxidized nor anti-oxidized low-density lipoprotein level is associated with atherosclerosis or mortality in hemodialysis patients

It is anticipated that oxidized low‐density lipoprotein (oxLDL) and anti‐oxLDL are associated with atherosclerosis and mortality. However, data on this issue are controversial and limited. We aimed to investigate the effect of these two markers on the extent and progression of atherosclerosis and mortality in a group of hemodialysis patients. In this prospective observational study with a follow‐up of 36 months, 124 hemodialysis patients were studied. Ninety‐five patients underwent carotid intima media thickness (CA‐IMT) measurement by B‐Mode ultrasonography both at baseline and at the end of the study. oxLDL and anti‐oxLDL were measured by enzyme‐linked immunosorbent assay. The extent and progression of CA‐IMT, along with overall and cardiovascular mortality, were assessed. The mean age at baseline was 54.0 ± 14.8 years, 57.3% male and 20% diabetic. The mean oxLDL and anti‐oxLDL levels were 8.11 ± 3.16 mU/L and 1.30 ± 0.31, respectively. Baseline mean CA‐IMT was 0.82 ± 0.20 mm. Fifteen patients died during a follow‐up period of 28.5 ± 6.6 months, 11 from cardiovascular causes. Only oxLDL, not anti‐oxLDL, was correlated with the extent of atherosclerosis at baseline. However, both had no role in the progression of atherosclerosis. Also, in unadjusted and adjusted models, both parameters were not associated with overall or cardiovascular mortality. Neither oxLDL nor anti‐oxLDL level is associated with the progression of atherosclerosis or mortality in hemodialysis patients.     

Synthesis and proton conductivity studies of methacrylate/methacrylamide‐based azole functional novel polymer electrolytes

Anhydrous polymer electrolytes based on azole functional methacrylates and methacrylamides have been produced for use in proton exchange membrane fuel cells (PEMFCs). Poly(methacryloyl chloride) (PMAC) was prepared first by free‐radical polymerization of methacryloyl chloride, followed by side chain functionalization with 5‐aminotetrazole (ATet), 3‐amino‐1,2,4‐triazole (ATri) and 1H‐1,2,4‐triazole (Tri). Finally, the obtained polymers were doped with triflic acid (TA) at stoichometric ratios of 1.0, 2.0 and 4.0 with respect to azole units, and the anhydrous polymer electrolytes were obtained. The membranes were characterized by FT‐IR, ¹³C‐NMR, and elemental analysis. Thermal behaviour of polymers was explored by TGA and DSC. The samples were thermally stable up to approximately 200 ^oC. Proton conductivity was measured by impedance spectroscopy. Trifilic acid doped poly(methacryloyl aminotetrazole) (PMAATet‐(TA)₄), poly(methacryloyl‐3‐amino‐1,2,4‐triazole) (PMA‐Tri‐(TA)₄), and poly(methacryloyl‐1,2,4‐triazole) (PMA‐ATri‐(TA)₄) showed maximum proton conductivities of 0.01 Scm^?1, 0.02 Scm^?1 and 8.7x10^?4 Scm^?1, respectively, at 150^°C and anhydrous conditions. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39915.     

The impact of anthropogenic and biogenic emissions on surface ozone concentrations in Istanbul

Surface ozone concentrations at Istanbul during a summer episode in June 2008 were simulated using a high resolution and urban scale modeling system coupling MM5 and CMAQ models with a recently developed anthropogenic emission inventory for the region. Two sets of base runs were performed in order to investigate for the first time the impact of biogenic emissions on ozone concentrations in the Greater Istanbul Area (GIA). The first simulation was performed using only the anthropogenic emissions whereas the second simulation was performed using both anthropogenic and biogenic emissions. Biogenic NMVOC emissions were comparable with anthropogenic NMVOC emissions in terms of magnitude. The inclusion of biogenic emissions significantly improved the performance of the model, particularly in reproducing the low night time values as well as the temporal variation of ozone concentrations. Terpene emissions contributed significantly to the destruction of the ozone during nighttime. Biogenic NMVOCs emissions enhanced ozone concentrations in the downwind regions of GIA up to 25 ppb. The VOC/NO_x ratio almost doubled due to the addition of biogenic NMVOCs. Anthropogenic NO_x and NMVOCs were perturbed by ± 30% in another set of simulations to quantify the sensitivity of ozone concentrations to the precursor emissions in the region. The sensitivity runs, as along with the model-calculated ozone-to-reactive nitrogen ratios, pointed NO_x-sensitive chemistry, particularly in the downwind areas. On the other hand, urban parts of the city responded more to changes in NO_x due to very high anthropogenic emissions.