644 research outputs found

    Adsorption of congo red from aqueous solution using rice husk, calcined kaolin clay, and microwaved rice husk clay hybrid

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    The present study focused on the comparative efficiency of rice husk (RH), calcined kaolin clay (CKC), and microwave rice husk clay hybrid (MRHCH) in the adsorption of congo red (CR) from aqueous solution. The rice husk was locally sourced and pulverized, the kaolin clay was calcined at 650 °C for two hours, while the rice husk clay hybrid was generated by microwave-impregnating an equal mixture of RH and CKC for 15 min at a medium temperature. The resulting adsorbents were characterized using scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy to evaluate their surface morphology and functional groups before and after adsorption. The effect of process variables comprising initial dye concentration, contact time, pH, and adsorbent dosage were investigated and the obtained adsorption equilibrium data were modelled using Langmuir, Temkin, and Freundlich isotherms. The adsorption kinetics were computed using Pseudo first order and Pseudo second-order reaction kinetics. The results of the study indicated that adsorption using all three adsorbents increased with increasing adsorbent dosage and contact time. On the other hand, adsorption using MRHCH and RH increased at a high initial concentration while CKC exhibited high adsorption at a low initial concentration. Isotherm studies indicated that Temkin isotherm best fits the adsorption equilibrium data while kinetic studies showed that the pseudo-second-order kinetic model best described CR adsorption, indicating chemisorption as the mechanism of adsorption. MRHCH demonstrated its exceptional adsorption capacity with a maximum adsorption capacity from the Langmuir isotherm of 4.008 mg/g. The adsorption process was found to be spontaneous, endothermic, and more random at the solid-solution interface by thermodynamic investigations. The study concludes that MRHCH has great promise for wastewater treatment applications as a very efficient adsorbent for CR removal

    Surface Composition of Pluto's Kiladze Area and Relationship to Cryovolcanism

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    A link between exposures of water (H2{}_{2}O) ice with traces of an ammoniated compound (e.g., a salt) and the probable effusion of a water-rich cryolava onto the surface of Pluto has been established in previous investigations (Dalle Ore et al. 2019). Here we present the results from the application of a machine learning technique and a radiative transfer model to a water-ice-rich exposure in Kiladze area and surroundings on Pluto. We demonstrate the presence of an ammoniated material suggestive of an undetermined but relatively recent emplacement event. Kiladze lies in a region of Pluto's surface that is structurally distinct from that of the areas where similar evidence points to cryovolcanic activity at some undetermined time in the planet's history. Although the Kiladze depression superficially resembles an impact crater, a close inspection of higher-resolution images indicates that the feature lacks the typical morphology of a crater. Here we suggest that a cryolava water carrying an ammoniated component may have come onto the surface at the Kiladze area via one or more volcanic collapses, as in a resurgent volcanic caldera complex. Large regions east of Kiladze also exhibit the presence of H2{}_{2}O ice and have graben-like structures suggestive of cryovolcanic activity, but with existing data are not amenable to the detailed search that might reveal an ammoniated component.Comment: 28 pages, 11 figures, submitted to Icaru

    Bicrossed products for finite groups

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    We investigate one question regarding bicrossed products of finite groups which we believe has the potential of being approachable for other classes of algebraic objects (algebras, Hopf algebras). The problem is to classify the groups that can be written as bicrossed products between groups of fixed isomorphism types. The groups obtained as bicrossed products of two finite cyclic groups, one being of prime order, are described.Comment: Final version: to appear in Algebras and Representation Theor

    Extending structures I: the level of groups

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    Let HH be a group and EE a set such that HEH \subseteq E. We shall describe and classify up to an isomorphism of groups that stabilizes HH the set of all group structures that can be defined on EE such that HH is a subgroup of EE. A general product, which we call the unified product, is constructed such that both the crossed product and the bicrossed product of two groups are special cases of it. It is associated to HH and to a system ((S,1S,),,,f)\bigl((S, 1_S,\ast), \triangleleft, \, \triangleright, \, f \bigl) called a group extending structure and we denote it by HSH \ltimes S. There exists a group structure on EE containing HH as a subgroup if and only if there exists an isomorphism of groups (E,)HS(E, \cdot) \cong H \ltimes S, for some group extending structure ((S,1S,),,,f)\bigl((S, 1_S,\ast), \triangleleft, \, \triangleright, \, f \bigl). All such group structures on EE are classified up to an isomorphism of groups that stabilizes HH by a cohomological type set K2(H,(S,1S)){\mathcal K}^{2}_{\ltimes} (H, (S, 1_S)). A Schreier type theorem is proved and an explicit example is given: it classifies up to an isomorphism that stabilizes HH all groups that contain HH as a subgroup of index 2.Comment: 17 pages; to appear in Algebras and Representation Theor

    Quaoar: New, Longitudinaly Resolved, Spectroscopic Characterization of Its Surface

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    (50000) Quaoar, one of the largest Trans-neptunian objects, is comparable in size to Pluto's moon Charon. However, while Charon's surface is rich almost exclusively in H2O ice, Quaoar's surface characterized by ices of CH4, N2, as well as C2H6, a product of irradiation of CH4 (Dalle Ore et al. 2009). Because of its distance from the Sun, Quaoar is expected to have preserved, to a degree, its original composition, however, its relatively small size did not make it a prime candidate for presence of volatile ices in the study by Schaller and Brown (2007). Furthermore, based on the Brown et al. (2011) study (Brown, Schaller, & Fraser, 2011. A Hypothesis for the Color Diversity of the Kuiper Belt. ApJL, 739, L60) its red coloration points to CH3OH as the ice which, when irradiated, might have produced the red material. We present new visible to near-infrared (0.3-2.48 micrometers) spectro-photometric data obtained with the XSHOOTER (Vernet et al. 2011, A&A, 536A, 105 ) instrument at the VLT-ESO facility at four different longitudes on the surface of Quaoar. The data are complemented by previously published photometric observations obtained in the near-infrared (3.6, 4.5 micrometers) with the Spitzer Space Telescope, which provide an extra set of constraints in the model calculation process in spite of the different observing times that preclude establishing the spatial consistency between the two sets. For each of the four spectra we perform spectral modeling of the entire wavelength range -from 0.3 to 4.5 micrometers- by means of a code based on the Shkuratov radiative transfer formulation of the slab model. We obtain spatially resolved compositional information for the surface of Quaoar supporting the presence of CH4 and C2H6, as previously reported, along with evidence for N2 and NH3OH. The albedo at the two Spitzer bands indicates the likely presence of CO and CO2. CH3OH, predicted on the basis of Quaoar's coloration (Brown et al. 2011), is not found at any of the four longitudes, implying that the presence of this ice is a sufficient, but not necessary condition for reddening of TNO surfaces. Other ices, in particular CH4 (Brunetto et al. 2006), have been shown to be plausible precursors for reddening of TNO surfaces

    An Election Energy Threshold Based Multi-Hop Routing Protocol in a Grid-Clustered Wireless Sensor Network

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    Owing to the limited energy of sensor nodes (SNs) in a wireless sensor network (WSN), it is important to reduce and balance the energy consumption of the SNs in order to extend the WSN lifetime. Clustering mechanism is a highly efficient and effective mechanism for minimizing the amount of energy that SNs consume during the transmission of data packets. In this paper, an election energy threshold based multi-hop routing protocol (mEEMRP) is presented. In order to minimize energy consumption, this routing protocol uses grid clustering, where the network field is divided into grid clusters. SNs in each grid cluster select a cluster head (CH) based on a weight factor that takes the node location, node’s residual energy (RE) as well as the node’s distance from the base station into consideration. An energy efficient multi-hop routing algorithm is adopted during the transmission of data packets from the cluster heads (CHs) to the base station (BS). This multi-hop routing algorithm uses an election energy threshold value, T­nhCH that takes into consideration the RE of CHs as well as the distance between CHs. Simulation results show a 1.77% and 10.65% improvement in terms of network lifetime for two network field scenarios over Energy Efficient Multi-hop Routing Protocol (EEMRP)

    Composition of KBO (50000) Quaoar

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    Aims. The objective of this work is to investigate the physical properties of objects beyond Neptune-the new frontiers of the Solar System-and in particular to study the surface composition of (50 000) Quaoar, a classical Transneptunian (or Kuiper Belt) object. Because of its distance from the Sun, Quaoar is expected to have preserved, to a degree, its original composition. Our goals are to determine to what degree this is true and to shed light on the chemical evolution of this icy body. Methods. We present new near-infrared (3.6 and 4.5 mu m) photometric data obtained with the Spitzer Space Telescope. These data complement high resolution, low signal-to-noise spectroscopic and photometric data obtained in the visible and near-infrared (0.4-2.3 mu m) at VLT-ESO and provide an excellent set of constraints in the model calculation process. We perform spectral modeling of the entire wavelength range-from 0.3 to 4.5 mu m by means of a code based on the Shkuratov radiative transfer formulation of the slab model. We also attempt to determine the temperature of H(2)O ice making use of the crystalline feature at 1.65 mu m. Results. We present a model confirming previous results regarding the presence of crystalline H(2)O and CH(4) ice, as well as C(2)H(6) and organic materials, on the surface of this distant icy body. We attempt a measurement of the temperature and find that stronger constraints on the composition are needed to obtain a precise determination. Conclusions. Model fits indicate that N(2) may be a significant component, along with a component that is bright at lambda > 3.3 mu m, which we suggest at this time could be amorphous H(2)O ice in tiny grains or thin grain coatings. Irradiated crystalline H(2)O could be the source of small-grained amorphous H(2)O ice. The albedo and composition of Quaoar, in particular the presence of N(2), if confirmed, make this TNO quite similar to Triton and Pluto
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