A spread slotted CDMA/ALOHA system with hybrid ARQ for satellitemultiple access

We propose and investigate a new type of satellite multiple access protocol that combines the characteristics of the spread slotted (SS)-ALOHA protocol, code division multiple access (CDMA), and the hybrid automatic repeat request (ARQ) error controlling and retransmission scheme, in order to increase the throughput by reducing the number of retransmissions and to keep the bit error rate (BER) of the satellite link low when the channel experiences heavy traffic. The main feature of our proposed system is the utilization of two different fields in the analysis of the satellite multiple access problem. Since the hub now possesses the forward error correction (FEC) capability to correct errors that appear after the CDMA despreading of the packets, the satellite does not need to ask so often for the retransmission of erroneous packets and will ask for retransmission only when the FEC error correcting capability is exceeded. This paper also presents the adaptive optimization of the balance between the CDMA processing gain and FEC coding gain in order to obtain a better throughput for the SS-CDMA/ALOHA with hybrid ARQ protocol for satellite multiple access. The optimization is made with the constraint of keeping the bandwidth of the transmitted packets constant during all times. According to this, the effective throughput of the protocol (information bits over total transmitted bits ratio) is improved by adaptively changing the CDMA and FEC codes used in the transmission. This adaptive optimization is done by observing the channel status or load and increasing or decreasing both coding schemes' gains. Computer simulations show the performance of the proposed multiple access scheme     

Lanthanides-clay nanocomposites: Synthesis, characterization and optical properties

Complexes of Europium(III) and Terbium(III) with 2,2-bipyridine and 1,10-phenanthroline were inserted into Na-bentonite by ion exchange reactions at room temperature. The products display interlaminar distances and stoichiometries in agreement with the ion exchange capacity and the interlayer space available in the clay. The optical properties of the intercalates, being qualitatively similar to those of the free complexes, are additionally improved with respect to exchange processes with the medium, especially in a moist environment. The protection again hydrolysis, together with the intensity of the optical transition ⁵D₀-⁵F₂ observed in the nanocomposite, makes these products promising for the development of novel optical materials.     

Impacts of gold nanoparticle exposure on two freshwater species: a phytoplanktonic alga (Scenedesmus subspicatus) and a benthic bivalve (Corbicula fluminea)

For years, nanotechnologies have developed the use of common materials, such as iron or silica, at an extremely small scale because of their new properties (reactivity, conductivity, optical sensitivity). More precisely, gold nanoparticles are used in numerous technologies such as electronics, new paints or research on cancer. But, despite their promising future and expansive utilization, only a few studies deal with their behaviors or impacts on the environment. Thus, we decided to explore the impacts of amine-coated 10nm gold nanoparticle (AuNp) contaminations on two freshwater aquatic models. The green algaScenedesmus subspicatus was submitted to 24 h-direct exposures at four AuNp concentrations (1.6×10², 1.6×10³, 1.6×10⁴ and 1.6×10⁵ AuNp/cell) along with a control condition. The process used for the freshwater bivalvesCorbicula fluminea was a trophic exposure during 7 days to three AuNp concentrations (1.6×10³, 1.6×10⁴ and 1.6×10⁵ AuNp/cell). These conditions were tested in triplicate with controls. For these experiments, OD measurements (γ= 520nm) were performed to verify AuNp concentrations in the water (stability). Cell numerations of algae were used to determine the growth/mortality effects on this species. Cellular impacts and AuNp distributions in the two species were revealed by transmission electron microscopy (TEM). The bioaccumulation rates were assessed by gold dosagesvia MS-ICP procedures. Molecular impacts were analyzed by quantifications of metallothionein concentrations (metal detoxification protein) and genetic expressions via real-time RT-PCR. Our study focused on the expression of six genes encoding proteins involved in: metal detoxification (metallothionein), the response to oxidative stress (catalase and superoxide-dismutase), the mitochondrial respiratory chain (subunit 1 of the cytochrome-C-oxidase), the concentration of mitochondria (RNA12s) and the response to xenobiotics (glutathione S transferase); using the β-actin as reference of the basal rates of gene expressions.     

Electrospinning of poly (2-ethyl-2-oxazoline)

Poly (2-ethyl-2-oxazoline) (PEOZ) is one of the commercial members of a family of materials that have shown significant application potential in a large number of technological contexts, most of them related with biomedical problems where water-soluble polymer systems are highly desirable. Polymeric fibers with diameters in the 200–800 nm range of PEOZ were prepared by electrospinning of its water solutions. Processing and solution parameters effects on the morphology and the diameter of the fibers were investigated. SEM results showed that the polymer concentration and the applied voltage might be used as variables to control the morphology and the diameter of the electrospun fibers. Solutions of the same polymer in other two organic solvents (N,N-dimethylformamide (DMF) and tetrahydrofurane (THF)) were also processed by the same technique but without the promising results of the water solutions.     

Stability of Pt-Ni/C (1:1) and Pt/C electrocatalysts as cathode materials for polymer electrolyte fuel cells: Effect of ageing tests

Carbon supported Pt and Pt-Ni (1:1) nanoparticles were prepared by reduction of metal precursors with NaBH₄. XRD analysis indicated that only a small amount of Ni alloyed with Pt (Ni atomic fraction in the alloy about 0.05). The as-prepared catalysts were submitted to chronoamperometry (CA) measurements to evaluate their activity for the oxygen reduction reaction (ORR). CA measurements showed that the ORR activity of the as-prepared Ni-containing catalyst was higher than that of pure Pt. Then, their stability was studied by submitting these catalysts to durability tests involving either 30 h of constant potential (CP, 0.8 V vs. RHE) operation or repetitive potential cycling (RPC, 1000 cycles) between 0.5 and 1.0 V vs. RHE at 20 mV s⁻¹. After 30 h of CP operation at 0.8 V vs. RHE, loss of all non-alloyed Ni, partial dissolution of the Pt-Ni alloy and an increase of the crystallite size was observed for the Pt-Ni/C catalyst. The ORR activity of the Pt-Ni/C catalyst was almost stable, whereas the ORR activity of Pt/C slightly decreased with respect to the as-prepared catalyst. Loss of all non-alloyed and part of alloyed Ni was observed for the Pt-Ni/C catalyst following repetitive potential cycling. Conversely to the results of 30 h of CP operation at 0.8 V vs. RHE, after RPC the ORR activity of Pt-Ni/C was lower than that of both as-prepared Pt-Ni/C and cycled Pt/C. This result was explained in terms of Pt surface enrichment and crystallite size increase for the Pt-Ni/C catalyst.     

Characterization of the lactic acid bacteria in ewe's milk and cheese from northwest Argentina

Indigenous lactic acid bacteria in ewe's milk and artisanal cheese were studied in four samples of fresh raw milk and four 1-month-old cheeses from the provinces of northwest Argentina. Mean growth counts on M17, MRS, and MSE agar media did not show significant differences (P < 0.05) in raw milk and cheeses. Isolates of lactic acid bacteria from milk were identified as Enterococcus (48%), lactococci (14%), leuconostocs (8%), and lactobacilli (30%). All lactococci were identified as Lactococcus lactis (subsp. lactis and subsp. cremoris). Lactobacilli were identified as Lactobacillus plantarum (92%) and Lactobacillus acidophilus (8%). Enterococci (59%) and lactobacilli (41%) were isolated from cheeses. L. plantarum (93%), L. acidophilus (5%), and Lactobacillus casei (2%) were most frequently isolated. L. lactis subsp. lactis biovar diacetylactis strains were considered as fast acid producers. L. lactis subsp. cremoris strains were slow acid producers. L. plantarum and L. casei strains identified from the cheeses showed slow acid production. The majority of the lactobacilli and Lactococcus lactis strains utilized citrate and produced diacetyl and acetoin in milk. Enzyme activities (API-ZYM tests) of lactococci were low, but activities of L. plantarum strains were considerably higher. The predominance of L. plantarum in artisanal cheese is probably important in the ripening of these cheeses due to their physiological and biochemical characteristics.     

An iterative thresholding algorithm for image segmentation

A thresholding technique is developed for segmenting digital images with bimodal reflectance distributions under nonuniform illumination. The algorithm works in a raster format, thus making it an attractive segmentation tool in situations requiring fast data throughput. The theoretical base of the algorithm is a recursive Taylor expansion of a continuously varying threshold tracking function.     

Histamine does not potentiate cyclic AMP-mediated amylase secretion in the guinea-pig pancreatic acinar cells

Some chemotherapeutic agents, as well as TNF and Fas, induce apoptotic cell death in tumor cells, but the cellular components involved in the process have not yet been identified. Interleukin 1 beta converting enzyme (ICE) is a mammalian homolog of CED-3, a protein required for programmed cell death in nematode Caenorhabditis elegans. We found that a selective inhibitor of ICE/ced 3 family proteases, benzyloxycarbonyl Asp CH2OC(O) 2 6,-dichlorobenzene (Z-Asp-CH2-DCB). completely blocked the apoptotic cell death of human leukemia cells caused by etoposide, camptothecin, 1-beta-D-arabinofuranosyl cytosine (Ara-C) and adriamycin. Moreover, in antitumor agent-treated U937 cells, an ICE-like (CPP32-like) protease was strongly activated. These results indicate that ICE/ ced 3 family proteases are involved in antitumor agent-induced apoptosis. Activation of ICE family proteases plays a key role in apoptosis. However, the subsequent mechanisms resulting in apoptosis are largely unknown. We identified actin as a substrate of ICE family proteases. Cleavage of actin and other substrate proteins by ICE family proteases could be critical in the ongoing process of antitumor agent-induced apoptosis in tumor cells.