1,721,074 research outputs found
Rapid palatal expansion in treatment of Class II malocclusions.
No full textA technique which combines the use of rapid maxillary expansion and fixed appliance in growing patients, is presented. The treatment in three patients with Class II division 1 malocclusion and different skeletal patterns is described, and relative advantages highlighted
Evolutionary game theoretical on-line event detection over tweet streams
No full textCurrent Online Social Networks represent a means for the continuous generation and distribution of information, which is slightly changed when moving from a user to another during the traversing of the network. Such an amount of information can overcome the capacity of a single user to manage it, so it would be useful to reduce it so that the user is able to have a summary of the information flowing the network. To this aim, it is of crucial importance to detect events within such an information stream, composing of the most representative words containing in each information instance, representing the event described by the set of tweet categorized together. There is a vast literature on off-line event detection on data-sets acquired from online social networks, but a similar solid set of approaches is missing if the detection has to be done on-line, which is demanding by the current applications. The driving idea described in this paper is to realize on-line clustering of tweets by leveraging on evolutionary game theory and the replicator dynamics, which have been used with success in many classification problems and/or multiobjective optimizations. We have adapted and enhanced a evolutionary clustering from the literature to meet the needs of on-line tweet clustering. Such a solution has been implemented according to the Kappa architectural model and assessed against state-of-the art approaches showing higher values of topic and keyword recall on two realistic data-sets
Random and Block Copolymers of Isotactic Polypropylene with Higher α-Olefins: The Role of the Chain Topology on the Side-Chains Confined Crystallization
No full textSamples of isotactic propylene-1-octadecene (iPP-co-C18) random copolymers and of diblock copolymers (BCPs) of isotactic polypropylene (iPP) linked to a propylene-1-octadecene block (P-co-C18), iPP-b-P(P-co-C18) with tuned block length and different comonomer content (up to 24 mol %) have been prepared using two different organometallic Hf-based catalysts. Both catalysts ensure good activity, high comonomer incorporation preserving high molecular weight, and a living behavior with the Cs-symmetric pyridylamido-Hf dimethyl complex. The influence of the copolymer topology with random and block architecture on the crystallization behavior and, specifically, the crystallization of side-chains has been analyzed. In random copolymers iPP-co-C18, the main-chains crystallize in the α form and in a mesophase of iPP, whereas at low temperature, the side-chains of the C18 co-units crystallize forming PE-like crystals. The crystallization of the lateral chains is surprisingly observed even in the sample with low C18 concentration and low branches’ frequency, where the randomly placed branches are highly spaced. This indicates that these random copolymers show unexpected nanophase separation between iPP chains and alkyl side-chains, with aggregation of side-chains that facilitates their crystallization even at low branches’ frequency. In the iPP-b-P(P-co-C18) BCPs, the iPP blocks crystallize in the common α form and the side-chains of the C18 co-units in the P(P-co-C18) block crystallize at low temperature, forming polyethylene-like crystals. The confined crystallization at low temperature of side-chains of the C18 co-units is driven by both phase separation of the dissimilar blocks (further driven by iPP crystallization) as well as by phase separation induced by the local incompatibility inside the P(P-co-C18) block between main-chain and C18 side-chains. This cooperative mechanism further facilitates the crystallization of the C18 side-chains compared to random copolymers and provides indirect evidence of microphase separation in these systems. We have demonstrated that branches are intriguingly segregated in nanodomains, favoring crystallization after self-aggregation, and can crystallize in random copolymers with a perfectly uniform and random distribution of C18 co-units even at very low comonomer content, therefore, even for low frequency of branching, when randomly placed branches are highly spaced
A less‐invasive approach with orthodontic treatment in Beckwith–Wiedeman patients
No full textthe beckwith-wiedemann syndrome (BWS) is a rare genetic disorder, linked to an alteration on the short arm of chromosome 11 that comprises multiple congenital anomalies. macroglossia is the predominant finding, with subsequent protrusion of dentoalveolar structures, which results in a protruding mandible, anterior open bite, abnormally obtuse gonial angle and increased mandibular length. a less-invasive treatment with orthopaedic appliances in a patient with early tongue reduction is presented. this work summarizes the oral signs linked to macroglossia, and highlights the influence of macroglossia on mandibular growth structures. In our opinion, glossotomy could be carried out in the paediatric patient as a preventive measure in that it curbs the tongue's influence on skeletal growth and dramatically reduces the duration and extensiveness of subsequent treatment
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
NEt3-Triggered Synthesis of UHMWPE Using Chromium Complexes Bearing Non-innocent Iminopyridine Ligands
No full textChromium complexes bearing non-innocent iminopyridine ligands were investigated as precatalysts for the polymerization of ethylene using different aluminum cocatalysts and Lewis base NEt3 as additive. Beyond confirming the key role of the chromium to ligand synergy in accessing the active complex, other factors that play a crucial role are (i) the nature of the aluminum activator that influences the ion pair generated, (ii) the presence of the additive that boosts the synthesis of UHMWPE with narrow and unimodal molecular weight distribution even at 40 °C, and (iii) the polymerization temperature that affects the polymerization catalysis and the polymer molecular weight. UV-vis-NIR and Fourier transform infrared (FT-IR) spectroscopic techniques have been applied to inspect the activation process and to understand the mode of action by which NEt3 affects the catalytic conversion of ethylene. NEt3 interacts with the aluminum cocatalyst (rather than with the chromium complex) to form an Et3N-AlRx adduct, thus affecting the catalytic ion pair
Extremophilic Microorganisms for the Green Synthesis of Antibacterial Nanoparticles
No full textThe biogenic synthesis of nanomaterials, i.e., synthesis carried out by means of living organisms, is an emerging technique in nanotechnology since it represents a greener and more eco-friendly method for the production of nanomaterials. In this line, in order to find new biological entities capable of biogenic synthesis, we tested the ability of some extremophilic microorganisms to carry out the biogenic production of AgNPs and SeNPs. Silver NPs were produced extracellularly by means of the thermophilic Thermus thermophilus strain SAMU; the haloalkaliphilic Halomonas campaniensis strain 5AG was instead found to be useful for the synthesis of SeNPs. The structural characterization of the biogenic nanoparticles showed that both the Ag and Se NPs possessed a protein coating on their surface and that they were organized in aggregates. Moreover, both types of NPs were found be able to exert an interesting antibacterial effect against either Gram-positive or Gram-negative species. This study confirmed that extremophilic microorganisms can be considered valuable producers of biologically active nanoparticles; nevertheless, further experiments must be performed to improve the synthesis protocols in addition to the downstream processes
Polymorphism and form II – form I transformation in Ziegler-Natta isotactic 1-butene-ethylene copolymers having a multiblock molecular structure
No full textA study of the crystallization behavior and kinetics of form II-form I transition in isotactic butene-ethylene copolymers (iPBEt) prepared with Ziegler-Natta catalyst with ethylene concentration in the range 9–44 mol% is presented. The samples have been separated with boiling solvents in different fractions containing chains with different ethylene concentration. Crystallization of form II from the melt is observed in each fraction even at high ethylene concentration, up to nearly 16 mol%. For higher ethylene content the samples do not crystallize from the melt but still crystallize during aging at room temperature in form I′. The comparison with the crystallization behavior of iPBEt copolymers prepared with homogeneous metallocene catalysts, characterized by a random distribution of ethylene units, has shown that the form II-form I transformation in Ziegler-Natta copolymers is much slower than in metallocene copolymers having the same ethylene concentrations and for the metallocene copolymers a low concentration of ethylene units of nearly 6 mol% is sufficient to prevent crystallization from the melt of form II. This indicates that in the chains of Ziegler-Natta iPBEt copolymers the regular butene sequences interrupted by the ethylene units are much longer than those of the chains of copolymers prepared with metallocene catalysts of the same ethylene concentration, giving further evidence of the multiblock structure of Ziegler-Natta iPBEt copolymers
Propylene-Butene Copolymers: Tailoring Mechanical Properties from Isotactic Polypropylene to Polybutene
No full textIsotactic propylene-butene copolymers [i(P-co-B)] with precise and controlled molecular structures were synthesized with various organometallic catalysts having different stereoselectivities. Stereoregular and stereodefective samples of i(P-co-B) with 1-butene (B) content variable in the whole range of composition were synthesized. All samples crystallize regardless of composition, indicating cocrystallization of propene and 1-butene units, which are incorporated in the unit cells of polymorphic forms of isotactic poly(propylene) (iPP) and isotactic poly(1-butene) (iPB). The copolymers show a continuum change of crystal morphology with the composition, transforming from big spherulites to bundle-like and needle-like crystals, to granular crystals. The cocrystallization allows maintaining high crystallinity of copolymers for any composition and provides an opportunity to develop outstanding mechanical properties that can be tailored by changing the isotacticity and composition. This allows, ideally, combining in the same material the different properties of stiffness of iPP and flexibility of iPB. These copolymers show, indeed, mechanical properties intermediate between iPP and iPB, ranging from stiffness/brittleness and ductility/flexibility depending on the composition and isotacticity, with high strength and Young's modulus that may be regulated by the stereoregularity of the iPP and iPB sequences, which is, in turn, dictated by the catalyst structure
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