Synthesis of cellular Si/SiC ceramics using native dicotyledonous plants was investigated. Mango (
Mangifera indica) represents a typical dicotyledonous plant. Wood of mango tree having typical ...structural features was transformed by controlled pyrolysis into carbonaceous preforms and subsequently converted into Si/SiC ceramics by liquid Si-infiltration at ∼1600
°C under vacuum. The pyrolyzed mango was characterized in terms of pyrolysis weight loss, shrinkages, bulk density and microstructures. The resulting ceramics have maximum density of 2.66
g/cm
3 with porosity of 0.5
vol.% and contain silicon carbide (SiC), residual Si, in addition to pores or carbon (trace). The conversion process preserves the microcellular morphology of the parent wood tissue anatomy in the ceramic structure. Typically, Si/SiC-mango has room temperature flexural strength of 247
MPa, Young's modulus of 253
GPa, hardness of 1182
kg/mm
2 and shows small gain in weight of ∼2% during oxidative heating up to 1300
°C in flowing air.
Woods from three dicotyledonous plants of local origin (mango
Mangifera indica), jackfruit (
Artocarpus integrifolia) and teak (
Tectona grandis) were transformed by pyrolysis into carbonaceous ...preforms and subsequently converted into cellular Si/SiC ceramics by liquid Si-infiltration and reaction. The pyrolyzed mango, jackfruit and teak were characterized in terms of pyrolysis weight loss, shrinkages, bulk density and microstructures. The Si-infiltrated pyrolyzed woods were found to have densities and porosities in the range of 2.46–2.60
gm
cm
−3 and 1.5–3.6
vol.% respectively. SEM imaging confirmed the preservation of microcellular tissue anatomy of the precursor wood structure in the morphologies of final ceramics. The end ceramics were investigated for the phases present and for crystallographic microtexture. A combination of XPS (X-ray photoelectron spectroscopy), XRD (X-ray diffraction) and OIM (orientation imaging microscopy) was used to establish the presence and the relative locations of silicon (Si), silicon carbide (SiC) and graphite (C). Fine SiC grains did typically surround coarse crystals of Si – the latter had significant presence of Σ3 twin boundaries. Graphite was primarily present in the regions containing SiC and was more textured than the SiC. Distinct orientation relationship could be established between the graphite crystals and the Si grains containing them.
Designing aluminum alloys for spall resistance requires an understanding of the active failure mechanisms under dynamic loading. However, it is time-consuming and expensive to obtain sufficient data ...to investigate these mechanisms from conventional plate impact spall experiments. Here we use a high-throughput laser-driven micro-flyer plate impact technique to connect the spall failure of aluminum alloy Al7085-T711 to its microstructure. By conducting tests at four impact velocities, we observe the full range of behaviors from incipient spall to complete spall failure. The spall strength of Al7085-T711 increases with both increasing strain rate and peak shock stress, as is typically the case in aluminum alloys. Examination of recovered samples indicates that incipient spall voids initiate primarily at Al7Cu2Fe second-phase particles. To further explore the effect of microstructure on spall failure, we annealed some specimens at 500°C to increase the aluminum grain size while retaining the Al7Cu2Fe particles, which had only a minor effect on spall strength. Solutionizing at 600°C to eliminate the Al7Cu2Fe second-phase particles, on the other hand, increases the spall strength significantly. Our results suggest that spall failure of Al7085-T711 is dominated by the presence Al7Cu2Fe second-phase particles, and that eliminating these particles could result in improved spall resistance of commercial alloys.
Three dicotyledonous woods of local origin mango (Mangifera indica), jackfruit (Artocarpus integrifolia) and teak (Tectona grandis) were transformed by pyrolysis into carbonaceous preforms and ...subsequently converted into cellular porous SiC ceramics by liquid Si infiltration under vacuum. The pyrolysed mango, jackfruit and teak were characterised in terms of pyrolysis weight loss, shrinkages, bulk density and microstructures. The end ceramics were light weight and found to have porosities in the range of 35·5-54·5 vol.-% depending on the preform carbon density and infiltration temperatures. Scanning electron microscope (SEM) imaging confirmed the preservation of cellular tissue anatomy of the precursor wood structure in the morphologies of final ceramics. The cellular porous SiC ceramics from mango, jackfruit and teak exhibited excellent oxidation resistance during heating to 1350°C in flowing air. Porous SiC mango gives the highest porosity with more than 80% pores being in the range of 0·5-11·58 μm and an average pore diameter of 7·82 μm, while the lowest porosity is obtained in the case of porous SiC jackfruit which has a mean pore diameter of 7 μm with ∼89% of pores in the range of 0·51-11·56 μm, indicating that the cellular porous SiC ceramic possesses application potential in the hot gas filtration area.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Air cooled condensers were first introduced in the US power industry in the early 1970s, but only during the last few decades has the number of installations greatly increased, largely to mitigate ...the problem of available water supply. Air may be used as a cooling medium in condensers where, primarily, there is scarcity of water, or where the ambient remains significantly cold for major parts of the year. Air cooled condensers are designed considering the design ambient conditions of summer. During winter months, if the air flow rate over the heat transfer surfaces is kept constant, it leads to improved condenser vacuum, and consequently, improved heat rate. Alternatively, the fans may be run at lower speeds, by using variable frequency drives (VFD), so as to keep the condenser vacuum constant, resulting uniform heat rate. This paper compares the economics between the power saved by the use of VFD in the condenser fans, keeping constant heat rate throughout the year, vis-à-vis, the saving in fuel, effected when the fans are operated at constant speed throughout the year and thus achieving improved heat rate during colder ambient.
Tumors of the broad ligament are uncommon. Leiomyoma, which is the commonest female genital neoplasm, is also the most common solid tumor of the broad ligament. Leiomyomas affect 30% of all women of ...reproductive age but the incidence of broad-ligament leiomyoma is <1%. These benign tumors are usually asymptomatic. A case is being described where a 52 year old presented with gradual abdominal swelling which was clinically and radiologically diagnosed as ovarian malignancy. On abdominal and bimanual palpation a soft cystic mass was noted in the right pelvic region. CA 125 was mildly raised. CEA, CA 19.9 levels were within normal limit. The radiological diagnosis was ovarian cyst with possibility of malignant changes. Staging laparotomy and histopathological examination of the resected specimen revealed a right sided broad ligament leiomyoma with cystic changes. The degenerative changes in the leiomyoma lead to the clinical and radiological diagnostic confusion. Thus, though uncommon, broad ligament leiomyoma should be considered during evaluation of adnexal masses for optimal patient management. The above description of leiomyoma in the broad ligament is a highly unique case and thus deserves appropriate attention.Kathmandu University Medical Journal Vol.12(3) 2014; 219-221
Pb(RaaiR′)(μ-X)2n (RaaiR′=1-alkyl-2-(arylazo)imidazole and X=Cl, Br, I) are structurally established. The complexes show E-to-Z (E, trans- and Z, cis-configuration) photoisomerization. The reverse, ...Z-to-E isomerization is feasible under thermal condition. Quantum yields (ϕE→Z) and activation energy (Ea) of Pb(RaaiR′)(μ-X)2n are less than free ligands. The rotor mass and volume control the isomerization rate. DFT computation has explained the spectroscopic and photochromic behavior. Display omitted
► Halide bridging Pb(II)-1-alkyl-2-(arylazo)imidazole Pb(RaaiR′)(μ-X)2n are described. ► The crystal structure of Pb(MeaaiMe)(μ-Cl)2n has confirmed bridged coordination polymer. ► The coordinated azoimidazole undergoes E-to-Z isomerization upon UV light irradiation. ► Quantum yields (ϕE→Z) of free ligand is higher than their coordinated phase in Pb(II) complex. ► DFT computation has explained the spectroscopic and photochromic behavior.
Halide bridging lead(II) coordination polymer of 1-alkyl-2-(arylazo)imidazole (RaaiR′), Pb(RaaiR′)(μ-X)2n is spectroscopically characterized and, the single crystal X-ray structure of Pb(MeaaiMe)(μ-Cl)2 (where MeaaiMe=1-methyl-2-(p-tolylazo)imidazole) has confirmed the structure. The UV light irradiation in DMF solution of the complexes shows E-to-Z (E and Z refer to trans and cis-configuration about –NN–, respectively) isomerization of the coordinated azoimidazole. The rate of isomerization follows: Pb(RaaiR′)(μ-Cl)2n<Pb(RaaiR′)(μ-Br)2n<Pb(RaaiR′)(μ-I)2n. Quantum yields (ϕE→Z) and the activation energy (Ea) of the isomerization of the complexes are lower than that of free ligand data. These may be due to increased mass and rotor volume of the complexes. The results are supported by DFT computation of optimized structures.
This note evaluates the usefulness of cointegration relations for estimating production function parameters, as pioneered by
Caballero (1994). While using long-run variation to estimate production ...function parameters is a desirable estimation strategy, this note demonstrates that the Cointegration Model will not be informative for estimating substitution parameters.
► Production function parameters are important for many economic issues. ► Tension exists between observed data and unobserved long-run values. ► Caballero’s Cointegration Model addresses this tension. ► This note evaluates the usefulness of cointegration relations in estimation. ► The Cointegration Model will not be informative for estimating substitution parameters.
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