The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform

Nevenka Kopjar - One of the best experts on this subject based on the ideXlab platform.

Martin Haenggi - One of the best experts on this subject based on the ideXlab platform.

  • Arbutus network layer load balancing for wireless sensor networks
    Wireless Communications and Networking Conference, 2008
    Co-Authors: Daniele Puccinelli, Martin Haenggi
    Abstract:

    The hot spot problem is a typical byproduct of the many-to-one traffic pattern that characterizes most wireless sensor networks: the nodes with the best channel to the sink are overloaded with traffic from the rest of the network and experience a faster energy depletion rate than their peers. Routing protocols for sensor networks typically use a reliability metric to avoid lossy links and thus directly exacerbate the problem. Significant advantages can be obtained by embedding a load balancing scheme at the network layer, as we show with the design and implementation of Arbutus, a novel routing protocol for wireless sensor networks with a built-in load balancing scheme. By imposing a special structure on the collection tree, privileging longer hops, and accounting for network load in the route selection process, Arbutus reduces the impact of hot spots on network lifetime without a deterioration of the end-to-end reliability performance. An implementation of Arbutus on Berkeley motes and the MoteLab testbed shows a 30% reduction in the network traffic load needed to achieve the same packet delivery rate as an existing mote-oriented protocol. This provides key benefits such as a significant lifetime gain and increased fault tolerance.

  • WCNC - Arbutus: Network-Layer Load Balancing for Wireless Sensor Networks
    2008 IEEE Wireless Communications and Networking Conference, 2008
    Co-Authors: Daniele Puccinelli, Martin Haenggi
    Abstract:

    The hot spot problem is a typical byproduct of the many-to-one traffic pattern that characterizes most wireless sensor networks: the nodes with the best channel to the sink are overloaded with traffic from the rest of the network and experience a faster energy depletion rate than their peers. Routing protocols for sensor networks typically use a reliability metric to avoid lossy links and thus directly exacerbate the problem. Significant advantages can be obtained by embedding a load balancing scheme at the network layer, as we show with the design and implementation of Arbutus, a novel routing protocol for wireless sensor networks with a built-in load balancing scheme. By imposing a special structure on the collection tree, privileging longer hops, and accounting for network load in the route selection process, Arbutus reduces the impact of hot spots on network lifetime without a deterioration of the end-to-end reliability performance. An implementation of Arbutus on Berkeley motes and the MoteLab testbed shows a 30% reduction in the network traffic load needed to achieve the same packet delivery rate as an existing mote-oriented protocol. This provides key benefits such as a significant lifetime gain and increased fault tolerance.

Karlo Jurica - One of the best experts on this subject based on the ideXlab platform.

Abdelkhaleq Legssyer - One of the best experts on this subject based on the ideXlab platform.

  • Effects of extracts and tannins from Arbutus unedo leaves on rat platelet aggregation.
    Phytotherapy research : PTR, 2006
    Co-Authors: Hassane Mekhfi, Abderrahim Ziyyat, Mohamed Bnouham, Mohammed Elhaouari, Mohammed Aziz, Abdelkhaleq Legssyer
    Abstract:

    Many cardiovascular diseases such as arterial hypertension are associated with an increase in blood platelet activity. Arbutus unedo (Ericaceae) is a medicinal plant reputed to treat arterial hypertension, so the present study was undertaken in order to determine the antiaggregant effect. The crude aqueous extract showed an inhibition of thrombin-induced platelet aggregation (IC50 = 1.8 ± 0.09 g/L, n = 10). The subsequent extraction of Arbutus unedo leaves by successive solvents showed that the methanol and ethyl acetate extracts accounted for most of the antiaggregant activity (IC50 = 0.7 ± 0.08, n = 9; 0.6 ± 0.05; n = 9, respectively). The tannins isolated from the methanol extract exhibited a strong antiplatelet effect (% of inhibition = 75.3 ± 1.4, n = 8) and may be the major chemical compounds responsible for this action. Our results support the traditional use of this plant in the preventive or therapeutic treatment of platelet aggregation linked to arterial hypertension. Copyright © 2006 John Wiley & Sons, Ltd.

  • Tannins and catechin gallate mediate the vasorelaxant effect of Arbutus unedo on the rat isolated aorta.
    Phytotherapy research : PTR, 2004
    Co-Authors: Abdelkhaleq Legssyer, Abderrahim Ziyyat, Mohamed Bnouham, Hassane Mekh, Christine Herrenknecht, Vincent Roumy, Christophe Fourneau, Alain Laurens, J. A. Hoerter, Rodolphe Fischmeister
    Abstract:

    This study examined the vascular effect of Arbutus leaves (aqueous extract) and described the isolation of several fractions responsible for their vasorelaxant activity. The aqueous extract (AE) of leaves was tested on rat aortic rings precontracted with 0.1 µm noradrenaline. At 10−2 g/L, AE produced an endothelium dependent relaxation of 66% ± 5%, (n = 8). The leaves of Arbutus were then extracted successively with different solvents and the methanol extract was the most active. When tannins (primarily condensed tannins) were precipitated from the methanol extract, they showed a strong vasorelaxant activity (87% ± 4%, n = 5), whereas the elimination of tannins in the methanol extract reduced significantly its vasorelaxant activity (42% ± 8%, n = 8, p < 0.005). The methanol extract was further separated semi-preparatively by reversed-phase HPLC. Four fractions (Fr2, Fr3, Fr4 and Fr6) were the most active and produced 88% ± 2% (n = 5), 75% ± 6% (n = 5), 76% ± 3% (n = 7) and 77% ± 3% (n = 10) relaxation, respectively. These four fractions mainly correspond to polyphenol compounds. Analysis of Fr6 indicated that this fraction contained catechin gallate. In conclusion, the vasorelaxant activity of Arbutus is likely to be due to polyphenol compounds, primarily condensed tannins and catechin gallate. Copyright © 2004 John Wiley & Sons, Ltd.

  • Arbutus unedo induces endothelium-dependent relaxation of the rat isolated aorta
    Phytotherapy Research, 2002
    Co-Authors: Abderrahim Ziyyat, Hassane Mekhfi, Mohamed Bnouham, Abdelhafid Tahri, Abdelkhaleq Legssyer, Jacqueline Hoerter, Rodolphe Fischmeister
    Abstract:

    Arbutus unedo L. (Ericaceae) is used in oriental Morocco to treat arterial hypertension. We studied its vasodilator effect and mechanisms of action in vitro. The root aqueous extract of Arbutus (0.25 mg/ml) produces a relaxation of noradrenalineprecontracted ring preparations of rat aorta with intact endothelium. Relaxation by Arbutus did not occur in specimens without endothelium and was inhibited by pretreatment with 100 µM N G-methyl-L-arginine (L-NMA), 10 µM methylene blue or 50 µM 1H-[1,2,4] oxadiazolo [4,3-a] quinoxaline-1-one (ODQ) but not by 10 µM atropine. These results suggest that Arbutus produces an endothelium-dependent relaxation of the isolated rat aorta which may be mediated mainly by a stimulation of the endothelial nitric oxide synthase by mechanisms other than activation of muscarinic receptors.

  • Arbutus unedo induces endothelium-dependent relaxation of the isolated rat aorta.
    Phytotherapy research : PTR, 2002
    Co-Authors: Abderrahim Ziyyat, Hassane Mekhfi, Mohamed Bnouham, Abdelhafid Tahri, Abdelkhaleq Legssyer, Jacqueline Hoerter, Rodolphe Fischmeister
    Abstract:

    Arbutus unedo L. (Ericaceae) is used in oriental Morocco to treat arterial hypertension. We studied its vasodilator effect and mechanisms of action in vitro. The root aqueous extract of Arbutus (0.25 mg/mL) produced a relaxation of noradrenaline-precontracted ring preparations of rat aorta with intact endothelium. Relaxation by Arbutus did not occur in specimens without endothelium and was inhibited by pretreatment with 100 μM NG-methyl-L-arginine (L-NMA), 10 μM methylene blue or 50 μM 1H-[1,2,4] oxadiazolo [4,3-a] quinoxaline-1-one (ODQ) but not by 10 μM atropine. These results suggest that Arbutus produces an endothelium-dependent relaxation of the isolated rat aorta which may be mediated mainly by a stimulation of the endothelial nitric oxide synthase by mechanisms other than activation of muscarinic receptors. Copyright © 2002 John Wiley & Sons, Ltd.

Hassane Mekhfi - One of the best experts on this subject based on the ideXlab platform.

  • Anti-platelet aggregation effects of extracts from Arbutus unedo leaves
    Plant Science Today, 2017
    Co-Authors: Mohammed El Haouari, Hassane Mekhfi
    Abstract:

    It is well known that platelet hyperactivity is a risk factor for cardiovascular diseases such as atherosclerosis, stroke and myocardial infarction. This study aimed to examine the effects of extracts enriched in flavonoids obtained from Arbutus unedo leaves on platelet aggregation. Rat platelets were prepared and incubated in vitro with different doses of the tested extracts, and aggregation was trigged by physiological agonists. Platelet treatment with increasing concentrations (0.1 - 1 mg/ml) of diethyl ether extract (genins = free flavonoids) or ethyl acetate extract (hetrosidic flavonoids) inhibited platelet aggregation evoked by thrombin in a concentration-dependant manner. The IC50 values were 0.22 ± 0.03 and 0.36 ± 0.05 mg/ml for genins and heterosidic flavonoids respectively. Treatment with Arbutus unedo extracts also significantly reduced the initial rate of platelet aggregation. At 1 mg/ml, the rate inhibition was 97.8 ± 0.74 and 90.8 ± 1.55 % for genins and heterosidic flavonoids respectively. In addition, flavonoids significantly inhibited platelet aggregation induced by ADP, collagen or epinephrine. We conclude that Arbutus unedo extracts show antiaggregant effects due mainly to flavonoids. These results may partly explain the traditional use of Arbutus unedo leaves for the treatment of cardiovascular disorders such as hypertension.

  • Antiaggregant effects of Arbutus unedo extracts in human platelets.
    Journal of ethnopharmacology, 2007
    Co-Authors: Mohammed El Haouari, Hassane Mekhfi, Jose J. Lopez, Juan A. Rosado, Ginés M. Salido
    Abstract:

    Abstract Platelet hyperaggregability plays a pivotal role in the pathogenesis of cardiovascular diseases. Thrombin evokes aggregation through Ca 2+ mobilization, tyrosine phosphorylation and generation of reactive oxygen species (ROS). We have investigated the antiaggregant properties of Arbutus unedo extracts in human platelets. Changes in cytosolic Ca 2+ concentration and intracellular oxidants production were registered by espectrofluorimetry using fura-2 and dichlorodihydrofluorescein, respectively, platelet aggregation was assessed by aggregometry and protein tyrosine phosphorylation was detected by Western blotting. Platelet treatment with increasing concentrations (0.015–1.5 mg/mL) of crude aqueous, ethyl acetate or diethyl ether extracts reduced platelet aggregation evoked by thrombin (0.5 U/mL) and show a potent ROS scavenger activity, preventing thrombin-evoked endogenous generation of ROS. Treatment with Arbutus unedo extracts did not alter thrombin-evoked Ca 2+ release from the intracellular stores but reduced store-operated Ca 2+ entry induced by thrombin or by selective depletion of the two Ca 2+ stores in platelets, the dense tubular system and the acidic stores. In addition, platelet treatment with extracts reduced both basal and thrombin-stimulated protein tyrosine phosphorylation. We conclude that Arbutus unedo extracts show antiaggregant actions due to attenuation of Ca 2+ mobilization, ROS production and protein tyrosine phosphorylation and might be used for the treatment and/or prevention of cardiovascular diseases.

  • Effects of extracts and tannins from Arbutus unedo leaves on rat platelet aggregation.
    Phytotherapy research : PTR, 2006
    Co-Authors: Hassane Mekhfi, Abderrahim Ziyyat, Mohamed Bnouham, Mohammed Elhaouari, Mohammed Aziz, Abdelkhaleq Legssyer
    Abstract:

    Many cardiovascular diseases such as arterial hypertension are associated with an increase in blood platelet activity. Arbutus unedo (Ericaceae) is a medicinal plant reputed to treat arterial hypertension, so the present study was undertaken in order to determine the antiaggregant effect. The crude aqueous extract showed an inhibition of thrombin-induced platelet aggregation (IC50 = 1.8 ± 0.09 g/L, n = 10). The subsequent extraction of Arbutus unedo leaves by successive solvents showed that the methanol and ethyl acetate extracts accounted for most of the antiaggregant activity (IC50 = 0.7 ± 0.08, n = 9; 0.6 ± 0.05; n = 9, respectively). The tannins isolated from the methanol extract exhibited a strong antiplatelet effect (% of inhibition = 75.3 ± 1.4, n = 8) and may be the major chemical compounds responsible for this action. Our results support the traditional use of this plant in the preventive or therapeutic treatment of platelet aggregation linked to arterial hypertension. Copyright © 2006 John Wiley & Sons, Ltd.

  • Arbutus unedo induces endothelium-dependent relaxation of the rat isolated aorta
    Phytotherapy Research, 2002
    Co-Authors: Abderrahim Ziyyat, Hassane Mekhfi, Mohamed Bnouham, Abdelhafid Tahri, Abdelkhaleq Legssyer, Jacqueline Hoerter, Rodolphe Fischmeister
    Abstract:

    Arbutus unedo L. (Ericaceae) is used in oriental Morocco to treat arterial hypertension. We studied its vasodilator effect and mechanisms of action in vitro. The root aqueous extract of Arbutus (0.25 mg/ml) produces a relaxation of noradrenalineprecontracted ring preparations of rat aorta with intact endothelium. Relaxation by Arbutus did not occur in specimens without endothelium and was inhibited by pretreatment with 100 µM N G-methyl-L-arginine (L-NMA), 10 µM methylene blue or 50 µM 1H-[1,2,4] oxadiazolo [4,3-a] quinoxaline-1-one (ODQ) but not by 10 µM atropine. These results suggest that Arbutus produces an endothelium-dependent relaxation of the isolated rat aorta which may be mediated mainly by a stimulation of the endothelial nitric oxide synthase by mechanisms other than activation of muscarinic receptors.

  • Arbutus unedo induces endothelium-dependent relaxation of the isolated rat aorta.
    Phytotherapy research : PTR, 2002
    Co-Authors: Abderrahim Ziyyat, Hassane Mekhfi, Mohamed Bnouham, Abdelhafid Tahri, Abdelkhaleq Legssyer, Jacqueline Hoerter, Rodolphe Fischmeister
    Abstract:

    Arbutus unedo L. (Ericaceae) is used in oriental Morocco to treat arterial hypertension. We studied its vasodilator effect and mechanisms of action in vitro. The root aqueous extract of Arbutus (0.25 mg/mL) produced a relaxation of noradrenaline-precontracted ring preparations of rat aorta with intact endothelium. Relaxation by Arbutus did not occur in specimens without endothelium and was inhibited by pretreatment with 100 μM NG-methyl-L-arginine (L-NMA), 10 μM methylene blue or 50 μM 1H-[1,2,4] oxadiazolo [4,3-a] quinoxaline-1-one (ODQ) but not by 10 μM atropine. These results suggest that Arbutus produces an endothelium-dependent relaxation of the isolated rat aorta which may be mediated mainly by a stimulation of the endothelial nitric oxide synthase by mechanisms other than activation of muscarinic receptors. Copyright © 2002 John Wiley & Sons, Ltd.