A correlation to describe interfacial heat transfer coefficient during solidification of Al–Si alloy casting

A thin wall Al–9 wt.% Si alloy casting was made in a sand mold prepared by CO₂ process. The thermal history obtained from the experiment was used to solve an inverse heat conduction problem (IHCP). The IHTC was estimated by an iterative algorithm based on the function specification method. Acquired IHTC values are given as a function of time and as a function of the casting surface temperature at the interface. It has been found that pattern of IHTC variation with casting surface temperature can be described by an equation which has been proposed as a new correlation model. In order to verify broader applicability of the proposed correlation, its use is demonstrated on the IHTC results taken from the literature.     

Influence of NaCl on Granulometric Characteristics and Polymorphism in Batch‐Cooling Crystallization of Glycine

The effect of NaCl added in different quantities on thermodynamic properties, granulometric characteristics, and structure of glycine in a crystallization process was investigated. Solubilities of α‐ and γ‐polymorphs in the presence of varying amounts of NaCl were analyzed. In order to examine the impact of the additive on granulometric properties of glycine, crystal morphology was examined by observing crystals under a scanning electron microscope. Crystal size distribution was determined by sieve analysis. By X‐ray diffraction analysis, the critical concentration of NaCl at which the structure of glycine changed, could be defined. The purity of obtained polymorphs was confirmed by Fourier transform infrared spectroscopy.     

Effects of access phases lengths on performance of IEEE 802.15.6 CSMA/CA

In this paper, we study interplay of prioritizing mechanisms in recently released IEEE 802.15.6 standard for Wireless Body Area Networks (WBANs). Among eight User Priorities (UPs) we study the impact of access phases lengths and CSMA/CA mechanism on the network performance. We consider a star-topology single-hop WBAN in which the hub operates in beacon mode with superframe boundaries. Our study is conducted in saturation regime and an error prone channel in order to indicate performance bounds for all UPs. We have developed an analytical model for the CSMA/CA-based Medium Access Control (MAC) layer of IEEE 802.15.6 which includes Markov chain and probabilistic models for all UPs. In order to validate the analytical model we have developed a simulation model in OPNET. We investigate the effectiveness of deploying exclusive access phases and second random access phase on the network performance. We also examine the medium utilization and normalized throughputs of all UPs. Obtained performance bounds indicate potential tradeoff between the prioritizing parameters which affect the saturation throughputs.     

Greening commercial air transportation by using liquid hydrogen (LH2) as a fuel

Global commercial air transportation has grown over the past two decades at a rather stable annual rate of 4.5–5% in the passenger and 6% in the cargo segment. Such developments have contributed to globalization of the economy and overall social welfare while at the same time increased impacts on the environment and society in terms of fuel consumption from non-renewable sources and related emissions of GHG (Green House Gases), land use, congestion, and local noise. In particular, further growth of emissions of GHG driven by growth of air transportation demand could contribute to global warming and consequent climate change.     

Energy thrift and improved performance achieved through novel railway brake discs

A disc with radial vanes and circumferential pillars proves to be successful in operation and achieves energy efficiency improvements compared with those of traditional design. Cooling characteristics of this novel design are practically identical to the disc with tangential vanes but the equivalent aerodynamic (air pumping) losses are approximately 50% less. It is shown that these reductions in pumping losses can lead to substantial energy savings in train operations.     

Chemical composition and antioxidant and antimicrobial activity of two Satureja essential oils

Hydro-distilled volatile oils from the aerial parts of Satureja montana L., and Satureja subspicata Bartl. ex Vis., growing wild in Bosnia and Herzegovina, were analyzed by GC/MS. More than one hundred compounds were identified in both plant oils, representing 92.4–98.1% of the total oil. The major constituents of essential oils obtained from the plant material of S. montana, collected from two different localities, were thymol (31.7%), and geraniol (22.3%), respectively. The most abundant compounds in essential oils of S. subspicata, collected at two different stages of development, were thymol (28.6%), and spathulenol (37.6%), respectively. The screening of antimicrobial activity of essential oil samples was individually evaluated against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Pseudomonas aeruginosa and Bacillus subtilis using a paper disc diffusion method. All tested microorganisms were inhibited by essential oil samples. Antioxidant activity was tested using the DPPH radical-scavenging method. All samples showed activity comparable to thymol, which was used as a positive probe.     

Surface modification of macroporous glycidyl methacrylate based copolymers for selective sorption of heavy metals

Two samples of macroporous poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate), poly(GMA-co-EGDMA), were synthesized by suspension copolymerization and modified with amines. Initial poly(GMA-co-EGDMA), and the samples modified with ethylene diamine [poly(GMA-co-EGDMA)-en], diethylene triamine [poly(GMA-co-EGDMA)-deta] and triethylene tetramine [poly(GMA-co-EGDMA)-teta], were characterized by mercury porosimetry, FTIR spectroscopy and elemental analysis. The most pronounced increase of specific surface area (75%) was observed for poly(GMA-co-EGDMA)-teta sample with smaller particles (D < 150 μm). The Cu(II) sorption was rapid, depending on porosity of amino-functionalized samples and ligand type. For poly(GMA-co-EGDMA)-deta and poly(GMA-co-EGDMA)-teta sorption half time required to reach 50% of total sorption capacity, t _1/2, were around 3 min. Sorption capacities for Cu(II), Co(II), Cd(II) and Ni(II) as well as for Cr(VI), Co(II), Cd(II) and Ni(II) ions were determined under competitive conditions as a function of pH, ligand type and porosity at room temperature. The results indicate selectivity of poly(GMA-co-EGDMA)-deta for Cu(II) over Cd(II) of 3:1 and for Cu(II) over Ni(II) and Co(II) of 6:1. The decrease in particle size of poly(GMA-co-EGDMA)-teta caused the increase of sorption capacities for all metal ions. At pH 1.8 the selectivity of poly(GMA-co-EGDMA)-teta with smaller particles for Cr(VI) over Ni(II), Co(II) and Cd(II) ions was 8.5:1.     

Alternating phenylenevinylene and thienylenevinylene copolymers with cyano groups: Synthesis,photophysics and photovoltaics

Two alternating conjugated copolymers TTP and TTT were synthesized by Heck coupling of 2,3-bis-(5-bromothiophene-2-yl)acrylonitrile with 1,4-dihexyloxy-2,5-divinylbenzene and 3-hexyl-2,5-divinylthiophene, respectively. The absorption spectra of the copolymers in THF solution showed three maxima around 270, 370 and 460 nm with optical band gaps of 2.30–2.34 eV. The electrochemically estimated band gaps of copolymers were 2.04–2.10 eV. The thin film absorption spectra were broad and extended about from 250 to 600 nm with a long wavelength maximum near 470 nm. The copolymers emitted yellow-orange light with maximum at 528–551 nm in THF solution and 567–610 nm in thin film. TTP showed the most red shifted emission maximum between the copolymers. The performance of the photovoltaic cells which were fabricated using blends of the copolymers with 6,6-phenyl C61-butyric acid methyl ester (PCBM) (1:1 and 1:4, w/w) as well as pure copolymers was investigated.