Multiple access techniques for broadband multimedia satellite networks

Access to multimedia services is currently being considered by both wireless and wireline operators. Although satellites cannot compete directly with other alternatives, they can provide benefits in certain niche markets due to their wide coverage area and distance insensitivity. It is the goal of these satellite operators to simultaneously maximize channel utility (and revenue) and to meet the stringent quality of service requirements of the new multimedia services. To achieve both of these objectives, an efficient multiple access (MAC) protocol is required. Satellite MAC protocols have traditionally been based either on fixed assignment (for voice and video) and/or random assignment (for data). The unique feature of the newer multimedia services is that they generate a mix of these three traffic types, and moreover the traffic is much burstier than originally expected. As a result, the traditional protocols fail to provide the required performance. This work addressed this issue by proposing two new schemes--one based on combined free/demand assignment multiple access (CFDAMA) with a multi-frequency time-division multiple access (MF-TDMA) frame, and the other based on flow controlled random access with a multi-code time-division multiple access (MC-TDMA) frame. Performance results (for jitter-tolerant packet delay and real-time loss probability) show that both techniques perform well in a bent-pipe environment. For an on-board processing system, both protocols can be adapted to deal with possible congestion at the output of the on-board baseband switch. Performance of the modified CFDAMA scheme is superior to that of a rate-based technique proposed in the literature. For the proposed MC-TDMA system, soft blocking and congestion are both handled by controlling packet transmissions through a simple flow control parameter. Performance evaluation of satellite multimedia networks is also a very important topic. Event-driven simulations (with OPNET) prove invaluable to evaluate protocol performance, but these have limitations with regards to flexibility and accuracy (especially in evaluating real-time loss probability). As a result, certain key measures were obtained through analysis. In particular, the Matrix Geometric approach was applied to the CFDAMA scheme to determine real-time loss probability and jitter-tolerant packet delay

Materiali nanostrutturati a base di copolimeri a blocchi per applicazioni in nanotecnologie

Il presente lavoro di tesi è incentrato sullo studio di nuovi materiali a base di copolimeri a blocchi amorfi e semicristallini. Tali studi hanno evidenziato come sia possibile controllare il tipo di nanostruttura che si ottiene per separazione di fase, attraverso il controllo della cristallizzazione, utilizzando tecniche innovative basate sulla solidificazione direzionale da solventi cristallizzabili e sulla cristallizzazione epitassiale su opportuni supporti. Sono stati studiati copolimeri a blocchi semiscristallini a base di polietilene (PE), polipropilene sindiotattico (sPP), poli(L-lattide) (PLLA) e poliossietilene (PEO). I copolimeri semicristallini a base di PE e sPP sono stati sintetizzati mediante nuovi catalizzatori metallorganici, ed è stato effettuato uno studio strutturale e morfologico su tutti i campioni. In particolare gli studi morfologici condotti su questi campioni hanno evidenziato come sia possibile controllare il tipo di nanostruttura che si ottiene per separazione di fase, attraverso il controllo della cristallizzazione in modo da indurre la formazione di nanostrutture orientate a morfologia lamellare con ordine direzionale e periodicità dei nanodomini dei due blocchi a lungo raggio. Oltre ai copolimeri a blocchi semicristallini sono stati studiati copolimeri formati da due blocchi amorfi, in particolare è stato studiato un copolimero costituito da un blocco di polistirene (PS) legato ad un blocco di polimetilmetacrilato (PMMA). E’ stato messo appunto un semplice metodo che permette di realizzare devices elettronici con funzioni di memoria utilizzando come layer attivo la matrice polimerica nanostrutturata generata dal copolimero a blocchi PS-b-PMMA

Chitosan-alginate microparticles of Andrographis paniculata and Annona muricata extracts for Controlled Release

This study investigates the properties of microparticles prepared from Andrographis paniculata (AP) and Annona muricata (AM) aqueous extracts for controlled release. Extracts obtained by maceration of the dried powdered plant leaves were microencapsulated by counterion coacervation method. Microcapsules were characterized using Fourier-transform infrared-spectroscopy (FTIR), x-ray difractometry (XRD) and differential scanning calorimetry (DSC).In vitro release studies were carried out at pH 1.2 for 2 h and 6.8 for a further 10 h. Release was monitored at274 and 230 nm for AM and AP, respectively. Encapsulation efficacy was less than 52% for AP and 70% for AM. In vitro drug release at pH 1.2 showed less than 40% release from the microcapsules after 2h while over 90% of extract was released after 6h at pH 6.8. Conventional capsules released the content within 1 h in simulated gastric fluid. FTIR, XRD and DSC results indicate the stable character of the extract within the microcapsules. Microencapsulation with chitosan- alginate controlled the release of Andrographis paniculata (AP) and Annona muricata (AM) aqueous extracts

Microencapsulated Garcinia kola and Hunteria umbellata Seeds Aqueous Extracts – Part 1: Effect of microencapsulation process.

Objective: This study investigates microcapsulated aqueous extracts of Garcinia kola (GK) and Hunteria umbellata (HU) seeds. Method: Extracts obtained after maceration of dried powdered seeds were prepared as microcapsules with chitosan-alginate by counterion coacervation method. Microcapsules were characterized using differential scanning calorimetry (DSC), x-ray diffractometry (XRD) and fourier transform infrared (FTIR) spectroscopy. In vitro release studies were carried out at pH 1.2 for 2 h and 6.8 for a further 10 h. Results: Between 20 and 50% extract release occurred from microcapsules after 2 h while conventional tablets released 100% after 1 h at simulated gastric pH. At pH 6.8, >80% of extract was released from microcapsules after 6 h. DSC revealed the presence of complex materials. XRD and FTIR showed stable character of the plant extracts within the microcapsules. Conclusion: Controlled release of aqueous extracts derived from these plants was achieved by microencapsulation and therefore can be developed as suitable delivery devices

Breaking Symmetry Rules Enhance the Options for Stereoselective Propene Polymerization Catalysis

An example of breaking "Ewen's symmetry rule" for olefin catalysis polymerization is proposed by DFT calculations. Catalyst precursors with Cs symmetry are suggested to promote the isotactic propene polymerization by a modification of the active site geometry obtained via coordination with AlH-alkyl species in solution. The origin of stereocontrol in olefin polymerization is due to a dual mechanism dictated by the chiral catalyst. These findings may expand the toolbox for promoting stereoselective olefin polymerization by transition metal catalysts

Nanometal Skin of Plasmonic Heterostructures for Highly Efficient Near-Field Scattering Probes

In this work, atomic force microscopy probes are functionalized by virtue of self-assembling monolayers of block copolymer (BCP) micelles loaded either with clusters of silver nanoparticles or bimetallic heterostructures consisting of mixed species of silver and gold nanoparticles. The resulting self-organized patterns allow coating the tips with a sort of nanometal skin made of geometrically confined nanoislands. This approach favors the reproducible engineering and tuning of the plasmonic properties of the resulting structured tip by varying the nanometal loading of the micelles. The newly conceived tips are applied for experiments of tip-enhanced Raman scattering (TERS) spectroscopy and scattering-type scanning near-field optical microscopy (s-SNOM). TERS and s-SNOM probe characterizations on several standard Raman analytes and patterned nanostructures demonstrate excellent enhancement factor with the possibility of fast scanning and spatial resolution <12 nm. In fact, each metal nanoisland consists of a multiscale heterostructure that favors large scattering and near-field amplification. Then, we verify the tips to allow challenging nongap-TER spectroscopy on thick biosamples. Our approach introduces a synergistic chemical functionalization of the tips for versatile inclusion and delivery of plasmonic nanoparticles at the tip apex, which may promote the tuning of the plasmonic properties, a large enhancement, and the possibility of adding new degrees of freedom for tip functionalization

Cryptides Identified in Human Apolipoprotein B as New Weapons to Fight Antibiotic Resistance in Cystic Fibrosis Disease

Chronic respiratory infections are the main cause of morbidity and mortality in cystic fibrosis (CF) patients, and are characterized by the development of multidrug resistance (MDR) phenotype and biofilm formation, generally recalcitrant to treatment with conventional antibiotics. Hence, novel eective strategies are urgently needed. Antimicrobial peptides represent new promising therapeutic agents. Here, we analyze for the first time the ecacy of three versions of a cryptide identified in human apolipoprotein B (ApoB, residues 887-922) towards bacterial strains clinically isolated from CF patients. Antimicrobial and anti-biofilm properties of ApoB-derived cryptides have been analyzed by broth microdilution assays, crystal violet assays, confocal laser scanning microscopy and scanning electron microscopy. Cell proliferation assays have been performed to test cryptide eects on human host cells. ApoB-derived cryptides have been found to be endowed with significant antimicrobial and anti-biofilm properties towards Pseudomonas and Burkholderia strains clinically isolated from CF patients. Peptides have been also found to be able to act in combination with the antibiotic ciprofloxacin, and they are harmless when tested on human bronchial epithelial mesothelial cells. These findings open interesting perspectives to cryptide applicability in the treatment of chronic lung infections associated with CF disease

Propylene–Butene Copolymers: Tailoring Mechanical Properties from Isotactic Polypropylene to Polybutene

Isotactic 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

Morphology of Isotactic Polypropylene–Polyethylene Block Copolymers Driven by Controlled Crystallization

A study of the morphology of diblock copolymers composed of two crystalline blocks of isotactic polypropylene (iPP) and polyethylene (PE) is shown. The samples form phase-separated structures in the melt because of the incompatibility between iPP and PE blocks. Cylindrical PE microdomains are visible at room temperature in the sample with a PE volume fraction of 26%, rapidly quenched from the melt in liquid nitrogen. In the quenched sample, PE crystallizes inside the PE cylindrical microdomains, whereas crystals of iPP are not visible in the iPP domains because the quenching prevents crystallization of the lamellar α form. Less rapid cooling of the melt produces, instead, breakout crystallization, where the phase-separated structure of the melt is destroyed by the slow crystallization of the α form of iPP and of PE. The succession of crystallization of iPP and PE and the resulting final morphology have been analyzed by inducing selective and different orientations of iPP and PE crystals through epitaxial crystallization onto the benzoic acid (BA) crystal substrate. Epitaxy produces oriented crystallization of iPP and PE, with a unique alignment of PE lamellar crystals and a double orientation of iPP crystals on to the (001) exposed face of BA. Epitaxy destroys the phase-separated structure of the melt and induces the formation of ordered lamellar nanostructures with alternated layers of iPP and PE, whose orientation is defined by the alignment of PE or iPP crystals, which, in turn, is determined by epitaxy. The results indicate that crystalline block copolymers offer the opportunity to create nanoscale patterns on thin films and improve the possibility of controlling the microstructure of block copolymers and the alignment of microdomains by controlling the crystallization process