323,565 research outputs found
System Identification for Experimental Study for Polymerization Catalyst Reaction in Fluidized Bed
Full text linkIn this work, system identification method is used to capture the reactor characteristics of production rate
of polyethylene (PE) based on published experimental data. The identification method is used to measure
the percentage effect on the production rate of PE by measuring the effect of input factors of temperature of
reaction, hydrogen concentration, and [Al]/[Ti] molar catalyst ratio. Temperature of reaction has big effects
equal 52.4 % on the output of the system and 47.6 % on interaction of the system's parameters compare to
other two factors. Also, hydrogen concentration has big effect equal 45.66 % on the output of the system and
14.7 % on interaction of the system's parameters. [Al]/[Ti] molar catalyst ratio has big effect on interaction
of the system equal 28.6 and 1.94 % on the output of the system but less than the reaction temperature and
hydrogen concentration. All these results depend on experiment results and these results are very
important in industrial plants. ©2011 BCREC UNDIP. All rights reserved
[How to Cite: Ahmmed S. Ibrehem. (2011). System Identification for Experimental Study for
Polymerization Catalyst Reaction in Fluidized Bed. Bulletin of Chemical Reaction Engineering & Catalysis,
6 (2): 137-146
Consiliorum Alexandri Tartagni ... liber tertius ... : postremò additamenta praestantiss. I.C. Marci Antonii Nattae.
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Natta horizontalis Karsch 1879
No full textNatta horizontalis Karsch, 1879 Natta horizontalis Karsch 1879: 362. Pochyta moschensis Caporiacco, 1947: 249, pl. 2, fig. 76 (D ♀), syn. n. For full reference list see World Spider Catalog (2021). Type material. Holotype of P. moschensis, female: TANZANIA: Moshi [Moschi in German], 3°20’S 37°20’E, Ran stream, leg. VI-VII.1906, leg. K. Kittenberger (HNHM). Remarks. The holotype of Pochyta moschensis is in good condition. There is no doubt that this specimen has been misidentified, and that in reality it is Natta horizontalis, common species in Africa. The first author knows N. horizontalis very well and redescribed it (Wesołowska 1993).Published as part of Wesołowska, Wanda & Szűts, Tamás, 2021, A revision of the genus Pochyta Simon, with descriptions of new species (Araneae: Salticidae: Thiratoscirtina), pp. 1-41 in Zootaxa 5052 (1) on page 38, DOI: 10.11646/zootaxa.5052.1.1, http://zenodo.org/record/556588
Natta horizontalis Karsch 1879
No full textNatta horizontalis Karsch, 1879 Natta horizontalis Karsch, 1879: 362; PrÓszyŃski 1985: 78; figs 32–37; PrÓchniewicz 1989: 218, figs 33–38; Wesołowska 1993: 25, figs 17–41; Wesołowska & Cumming 2008: 201, figs 107–109; Wesołowska & Haddad 2009: 65; Haddad & Wesołowska 2011: 89, figs 102, 103. Cyllobelus rufopictus Simon, 1909: 420; Berland & Millot 1941: 320, fig. 22; Lawrence 1942: 187, fig.32. Cylobellus tristellatus Simon, 1906: 1171; Lessert 1936: 289, fig. 84. Natta tristellata PrÓszyŃski, 1985: 83, figs 42–44. Natta rufopicta PrÓszyŃski, 1985: 83, figs 46, 47. Wesołowska (1993) described both sexes. Material examined: Butha-Buthe district: 1♀ Valley near Butha-Buthe, 28°48'S 28°17'E, 1950 m, under rocks, grassland, 14.iii.2013, leg. J. van Niekerk (NCA 2013 /3112). Maseru district: 1♂ Mohale Dam, Islands, 29°25'S 28°06'E, under rocks, 14.xii.2003 (NCA 2013 /3093); 2♀ Same locality, 16.xii.2003 (NCA 2013 /3094). Quthing district: 1♂ Near Ha Liphapang village, 30°27'S 28°00'E, 1660 m, under rocks near Sebapela River, 15.xi.2003 (NCA 2013 /3095). Distribution: A species common in the Afrotropical Region. Recorded from scattered localities throughout Lesotho (Fig. 93).Published as part of Wesołowska, Wanda & Haddad, Charles R., 2014, An overview of the jumping spiders of Lesotho (Araneae: Salticidae), with descriptions of six new species, pp. 229 in African Invertebrates 55 (2) on page 255, DOI: 10.5281/zenodo.768093
Accretion in the ρ-Ophiuchi pre-main sequence stars
No full textAims.The aim of this paper is to provide a measurement of the mass accretion rate in a large, complete sample of objects in the core of the star forming region ρ Oph.
Methods: .The sample includes most of the objects (104 out of 111) with evidence of a circumstellar disk from mid-infrared photometry; it covers a stellar mass range from about 0.03 to 3 M_⊙ and it is complete to a limiting mass of 0.05 M_⊙. We used J and K-band spectra to derive the mass accretion rate of each object from the intensity of the hydrogen recombination lines, Paβ or Brγ. For comparison, we also obtained similar spectra of 35 diskless objects.
Results: .The results show that emission in these lines is only seen in stars with disks, and can be used as an indicator of accretion. However, the converse does not hold, as about 50% of our disk objects do not have detectable line emission. The measured accretion rates show a strong correlation with the mass of the central object (dot M_acc ∝ M_star1.8±0.2) and a large spread, of two orders of magnitude at least, for any interval of M_star. A comparison with existing data for Taurus shows that the objects in the two regions have similar behaviour, at least for objects more massive than ∼ 0.1 M_⊙. The implications of these results are briefly discussed
Il foulard - Fenomenologia di un accessorio
No full textSaggio sulla storia e l'iconografia del foular
Natta chionogaster
No full textNatta chionogaster (Simon, 1901) Cyllobelus chionogaster Simon, 1901 b: 151; Peckham & Peckham 1903: 195, pl. 21, fig. 1; Simon 1909:419. Cyllobelus australis Peckham & Peckham, 1903: 194, pl. 21, fig. 2. Natta chionogastra: PrÓszyŃski 1985: 80, figs 39–41, 45, 47; Wesołowska 1993: 18, figs 1–16; Haddad & Wesołowska 2011: 89, figs 74, 75. Wesołowska (1993) described both sexes. Material examined: Butha-Buthe district: 1♀ Butha-Buthe, 28°46'S 28°14'E, 1780 m, under rocks, sandstone ridge, 14.xii.2012, leg. J. van Niekerk (NCA 2013 / 2355), 3♂ (NCA 2013 / 2372). Qacha’s Nek district: 1♂ 1 imm. Near Maghoareng village, 30°03'S 28°53'E, 2200 m, under rocks on mountainside, 6.xi.2003 (NCA 2013 / 3092); 1♀ Sehlabathebe National Park, 29°53'S 29°07'E, 2940 m, under rocks, mountainside, 15.i.2013, leg. J. van Niekerk (NCA 2013 / 2381). Distribution: A species known from the Democratic Republic of Congo, Namibia and South Africa. Recorded here from three localities in eastern Lesotho (Fig. 93).Published as part of Wesołowska, Wanda & Haddad, Charles R., 2014, An overview of the jumping spiders of Lesotho (Araneae: Salticidae), with descriptions of six new species, pp. 229 in African Invertebrates 55 (2) on page 255, DOI: 10.5281/zenodo.768093
Accretion properties of T Tauri stars in σ Orionis
No full textAccretion disks around young stars evolve in time with time scales of a few million years. We present here a study of the accretion properties of a sample of 35 stars in the ∼ 3 million-year-old star-forming region σ Ori. Of these, 31 are objects with evidence of disks, based on their IR excess emission. We use near-IR hydrogen recombination lines (Paγ) to measure their mass accretion rate. We find that the accretion rates are significant lower in σ Ori than in younger regions, such as ρ Oph, consistently with viscous disk evolution. The He I 1.083 μ m line is detected (either in absorption or in emission) in 72% of the stars with disks, also providing evidence of accretion-powered activity in very low accretors, where other accretion indicators disappear
A search for clustering around Herbig Ae/Be stars
No full textWe present the results of new near-infrared observations of the fields around a sample of 19 Herbig Ae/Be stars. The observations reveal the population of young stars that accompanies the formation of intermediate-mass stars. The richness of the detected star clusters is investigated. We find a clear dependence of the richness of the cluster on the spectral type of the Herbig Ae/Be star, confirming that the mode of formation of intermediate-mass stars represents the transition between the high-mass and the low-mass modes. In particular, we find that the cluster nature of star formation appears at a significant (i.e. detectable) level for stars of B7 spectral type or earlier
Accretion in ρ Ophiuchus brown dwarfs: infrared hydrogen line ratios
No full textContext: .Mass accretion rate determinations are fundamental for an understanding of the evolution of pre-main sequence star circumstellar disks.
Aims: .Magnetospheric accretion models are used to derive values of the mass accretion rates in objects of very different properties, from brown dwarfs to intermediate-mass stars; we test the validity of these models in the brown dwarf regime, where the stellar mass and luminosity, as well as the mass accretion rate, are much lower than in T Tauri stars.
Methods: .We have measured nearly simultaneously two infrared hydrogen lines, Paβ and Brγ, in a sample of 16 objects in the star-forming region ρ-Oph. The sample includes 7 very low mass objects and brown dwarfs and 9 T Tauri stars.
Results: .Brown dwarfs where both lines are detected have a ratio Paβ/Brγof ~2. Larger values, ⪆3.5, are only found among the T Tauri stars. The low line ratios in brown dwarfs indicate that the lines cannot originate in the column of gas accreting from the disk onto the star along the magnetic field lines, and we suggest that they form instead in the shocked photosphere, heated to temperatures of ~3500 K. If so, in analogy to veiling estimates in T Tauri stars, the hydrogen infrared line fluxes may provide a reliable measure of the accretion rate in brown dwarfs
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