Future generation wireless multimediacommunications will require efficient Medium AccessControl (MAC) protocols able to guarantee suitable Qualityof Service (QoS) levels for different traffic classes whileachieving a high utilization of radio resources. This paperproposes a new scheduling technique to be adopted at the MAClevel in wireless access systems, named Dynamic Scheduling-Time DivisionDuplexing (DS-TDD), that efficiently managesvideo, voice, Web and background traffics. A theoretical approachis proposed in this paper to evaluate the DS-TDD performance withvoice and Web traffics. Simulation results have permitted tohighlight the following promising characteristics of the DS-TDDscheme: (i) a high capacity of real-time traffics isattained with a QoS insensitive to Web and background trafficloads; (ii) a high throughput can be guaranteed whilepreserving the QoS levels of the different traffic classes;(iii) heavier downlink traffic loads do not modify the QoSof uplink traffics. Finally, extensive comparisons with differentscheduling schemes proposed in the literature have permitted tohighlight the better performanceof DS-TDD. 相似文献
Inorganic–organic hybrid materials are attracting a strong scientific interest mainly for their outstanding inherent mechanical and thermal properties, which can be traced back to the intimate coupling of both inorganic and organic components. By carefully choosing the experimental parameters used for their synthesis, chemically and thermally stable acrylate-based hybrid material embedding the zirconium oxocluster Zr4O4(OMc)12, where OMcCH2C(CH3)C(O)O, can be deposited as UV-cured films on aluminium alloys.
In particular, the molar ratios between the oxocluster and the monomer, the polymerisation time, the amount of photo-initiator and the deposition conditions, by using an home-made spray-coating equipment, were optimised in order to obtain the best performing layers in terms of transparency and hardness to coat aluminium alloy (AA1050, AA6060 and AA2024) sheets. Furthermore, it was also evaluated whether the hybrid coatings behave as barrier to corrosion.
Several coated samples were prepared and characterised. Environmental scanning electronic microscopy (ESEM) and scratch test were used to investigate the morphology of the films and to evaluate their scratch resistance, respectively. Electrochemical impedance spectroscopy (EIS) was performed in order to evaluate if the coatings actually protect the metallic substrate from corrosion.
In order to measure shear storage modulus (G′) and loss modulus (G″) of the materials used for coatings, bulk samples were also obtained by UV-curing of the precursors solution. Dynamical mechanical thermal analysis (DMTA) was performed in shear mode on cured disks of both the hybrid materials and pristine polymer for comparison. The values of Tg were read off as the temperatures of peak of loss modulus. The length and mass of all the samples were measured before and after the DMTA analysis, so that the shrinkage of the materials in that temperature range was exactly evaluated. 相似文献
Human natural killer (NK) cells express inhibitory receptors that are specific for different groups of HLA-C or HLA-B alleles. The majority of these receptors belong to the immunoglobulin (Ig) superfamily and are characterized by two or three extracellular Ig-like domains. Here we describe a novel inhibitory NK receptor that is specific for a group of HLA-A alleles. The HLA-A3-specific NK cell clone DP7 has been used for mice immunization. Two mAbs, termed Q66 and Q241, bound to the immunizing clone and stained only a subset of NK cell populations or clones. Among Q66 mAb-reactive clones, we further selected those that did not express any of the previously identified HLA-class I-specific NK receptors. These clones did not lyse HLA-A3+ (or -A11+) target cells, but lysis of these targets could be detected in the presence of Q66 or Q241 mAbs. On the other hand, target cells expressing other HLA-A alleles, including -A1, -A2, and -A24, were efficiently lysed. Moreover, none of the HLA-C or HLA-B alleles that were tested exerted a protective effect. Q66+, but not Q66- NK cell clones, expressed messenger RNA coding for a novel 3 Ig domain protein homologous to the HLA-C (p58) and HLA-B (p70) receptors. The corresponding cDNA (cl.1.1) was used to generate transient and stable transfectants in COS7 and NIH3T3 cell lines, respectively. Both types of transfectants were specifically stained by Q66 and Q241 mAbs. Since the cytoplasmic tail of Q66-reactive molecules was at least 11 amino acid longer than the other known p58/p70 molecules, we could generate an antiserum specific for the COOH-terminus of Q66-reactive molecules, termed PGP-3. PGP-3 immunoprecipitated, only from Q66+ NK cells, molecules displaying a molecular mass of 140 kD, under nonreducing conditions, which resolved, under reducing conditions, in a 70-kD band. Thus, differently from the other p58/p70 receptors, Q66-reactive molecules appear to be expressed as disulphide-linked dimers and were thus termed p140. The comparative analysis of the amino acid sequences of p58, p70, and p140 molecules revealed the existence of two cysteins proximal to the transmembrane region, only in the amino acid sequence of p140 molecules. 相似文献
Polyolefins functionalized with diethylmaleate were mixed with poly(vinylchloride) (PVC) in different compositions. Intermolecular interactions involving the carbonyl groups of the side chains of the functionalized polyolefins and methine hydrogens of PVC were investigated by means of infrared spectroscopy. The major flexibility of the ester groups attached to the backbone chains, with respect to polyesters, seems to increase the capability of such groups to interact with groups of more polar polymers, thus allowing prediction of easier miscibility, which however also depends on the starting polyolefin structure and function-alization degree. 相似文献
Mobile networks are becoming nothing but a way to allow ubiquitous access to multimedia services. To allow efficient use of
resources, new systems provide flexible bandwidth and different error protection techniques to match channel behavior. As
the backbone network is increasingly becoming based on packet techniques and in particular on IP and related transport protocols,
end to end service quality must be analyzed considering both the fixed and the mobile part. Source scalability may help in
coping with a mixed and heterogeneous environment. In this work we present some results of a transmission chain comprising
a scalable MPEG-2 coder, an IP network and a radio access exploiting the availability of satellites. It is shown that for
a given target rate, differentiated coding can be exploited to achieve decodability and good quality at a channel SNR much
lower that single layer streams.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
Blood concentration of endogenous beta-endorphines can change during the clinical evolution of chronic bronchopneumopathies. The authors assessed the beta-endorphine concentrations in the pulmonary arterial and systemic arterial blood in 8 asthmatic patients during a symptom-free period and after methacholine-induced bronchospasm. The beta-endorphine analysis was performed in duplicate dor each sample, by means of a RIA assay. There is not difference in the systemic arterial blood concentration of beta-endorphines between asthmatic patients and normal subjects. Furthermore, there is no change in the beta-endorphine blood concentration during the passage through the pulmonary tissue after methacoline-induced bronchospasm. 相似文献
Alumina membranes were fabricated by anodizing aluminium metal in 0.15 M oxalic acid. The growth kinetics of the porous layer were investigated in the temperature range –1 to 16 °C using linear potential scans up to 70 V. The faradaic efficiencies of metal oxidation and of porous layer formation, determined by applying Faraday's law, were found to be independent of both temperature and electrical charge. SEM analysis of the metal-side and solution-side surfaces revealed different morphologies. After dissolution of the barrier layer in phosphoric acid, the metal-side surface showed circular pores whose size of about 90 nm was found to be uniform and independent of temperature. The pore population was also practically independent of temperature and a value of about 4 × 1013 pores m–2 was determined. On the solution-side surface the presence of a deposit partially occluding the mouths of pores was observed. This coating could be removed by chemical etching in NaOH or thermal treatment at 870 °C, where decomposition of oxalate occurs. This supports the hypothesis that the deposit consists of an aluminium salt containing oxalate anions precipitated from the solution. The results show that it is possible to control the morphological characteristics of the anodic alumina membranes by careful choice of experimental conditions. 相似文献
The oxidative dehydrogenation of ethane is carried out in short contact time reactors over Pt and LaMnO3 based catalysts supported on a large number of different ceramic substrates (45, 60 and 80 ppi foam monoliths and 200, 400, 600, 900 and 1200 cpsi honeycomb monoliths). Experimental results, obtained under the same conditions at varying the C2H6/O2 ratio, showed that the highest performance in terms of ethylene selectivity and yield is always attained on LaMnO3 catalysts. Furthermore, the results are significantly influenced by the morphology and cell density of the support, with 45 and 60 ppi foams and 400 and 600 cpsi honeycombs giving the best performance. The experimental results are explained by means of geometrical and fluid dynamic considerations on the support, and by means of a 2D mathematical model, which clearly indicates an optimal intermediate cell density for maximising ethylene selectivity and yield. 相似文献