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Current Threshold (current + threshold)

Distribution by Scientific Domains

Medical Sciences	54%
Life Sciences	36%

Selected Abstracts

Error-aware and energy-efficient routing approach in MANETs

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 1 2009
Liansheng Tan
Abstract The lifetime of a network is the key design factor of mobile ad hoc networks (MANETs). To prolong the lifetime of MANETs, one is forced to attain a tradeoff of minimizing the energy consumption and load balancing. In MANETs, energy waste resulting from retransmission due to high bit error rate (BER) and high frame error rate (FER) of wireless channel is significant. In this paper, we propose two novel protocols termed multi-threshold routing protocol (MTRP) and enhanced multi-threshold routing protocol (EMTRP). MTRP divides the total energy of a wireless node into multiple ranges. The lower bound of each range corresponds to a threshold. The protocol iterates from the highest threshold to the lowest one and chooses those routes with bottleneck energy being larger than the current threshold during each iteration. This approach thus avoids overusing certain routes and achieves load balancing. If multiple routes satisfy the threshold constraint, MTRP selects a route with the smallest hop count to further attain energy efficiency. Based on MTRP, EMTRP further takes channel condition into consideration and selects routes with better channel condition and consequently reduces the number of retransmissions and saves energy. We analyze the average loss probability (ALP) of the uniform error model and Gilbert error model and give a distributed algorithm to obtain the maximal ALP along a route. Descriptions of MTRP and EMTRP are given in pseudocode form. Simulation results demonstrate that our proposed EMTRP outperforms the representative protocol CMMBCR in terms of total energy consumption and load balancing. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Systematic evaluation of the highest current threshold for regional anaesthesia in a porcine model

ACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 6 2010
T. STEINFELDT
Background: The purpose of this study was to determine systematically the highest minimal stimulation current threshold for regional anaesthesia in pigs. Methods: In an established pig model for regional anaesthesia, needle placements applying electric nerve stimulation were performed. The primary outcome was the frequency of close needle to nerve placements as assessed by resin injectates and subsequent anatomical evaluation. Following a statistical model (continual reassessment method), the applied output currents were selected to limit the necessary number of punctures, while providing guidance towards the highest output current range. Results: Altogether 186 punctures were performed in 11 pigs. Within the range of 0.3,1.4 mA, no distant needle to nerve placement was found. In the range of 1.5,4.1 mA, 43 distant needle to nerve placements occurred. The range of 1.2,1.4 mA was the highest interval that resulted in a close needle to nerve placement rate of ,95%. Conclusions: In the range of 0.3,1.4 mA, all resin deposition was found to be adjacent to nerve epineurium. The application of minimal current intensities up to 1.4 mA does not obviously lead to a reduction of epineural injectate contacts in pigs. These findings suggest that stimulation current thresholds up to 1.4 mA result in equivalent needle tip localisation in pigs. [source]

High or low current threshold for nerve stimulation for regional anaesthesia

ACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 10 2009
T. STEINFELDT
Background: The purpose of this study was to determine whether the application of high stimulation current thresholds (SCT) leads to a distant needle to nerve proximity (NNP) compared with low SCT during nerve localization for regional anaesthesia in pigs. Methods: A minimal motor response to the stimulation of femoral or brachial plexus nerves in 16 anaesthetized pigs was triggered either by a minimal SCT of a low (0.01,0.3 mA) or a high (0.8,1.0 mA) current in a random order. After eliciting a motor response with a predetermined SCT, synthetic resin was injected via the needle. After postmortem dissection of the injection site, the localization of the resin deposition was determined verifying the final position of the needle tip. Depending on the proximity of resin deposition to the nerve epineurium, the needle tip placement was considered either as a close or a distant NNP. Results: A total of 235 punctures were performed. Ninety-one punctures were carried out with low SCT and 92 with a high SCT. Fifty-two punctures served as a control (1.8,2.0 mA). All injectates following both high or low SCT were considered ,close needle tip to nerve placement', whereas 27 of 52 injectates of the control group appeared distant to nerve epineurium. Conclusion: Regardless of the applied SCT, i.e. high or low, all resin deposition was found adjacent to nerve epineurium. These findings suggest that high and low SCT result in equivalent needle tip localization in pigs. [source]

Ultrasensitive assessment of residual HIV viraemia in HAART-treated patients with persistently undetectable plasma HIV-RNA: A cross-sectional evaluation

JOURNAL OF MEDICAL VIROLOGY, Issue 3 2009
Stefano Bonora
Abstract Improvements in HIV-RNA assays have made accurate detection of as few as 2 copies/ml possible. This study objective was the evaluation of ultrasensitive HIV-RNA quantitation (beneath current threshold: 50 copies/ml) in patients receiving different antiretroviral regimens. A cross-sectional, ultrasensitive measurement of HIV-RNA levels (detection limit: 2.5 HIV-RNA copies/ml) was performed in 154 HIV-1-infected patients receiving ARV therapy, all classed as full responders according to the 50 copies/ml cut-off. Patients were undergoing treatment with two nucleoside/nucleotide reverse transcriptase inhibitors (N/NtRTIs) plus nevirapine (NVP, n,=,48), efavirenz (EFV, n,=,57) or lopinavir/ritonavir (LPV/r, n,=,49). Undetectable HIV-RNA (<2.5 copies/ml) occurred in 29/48 (60.4%), 24/57 (42.1%) and 14/49 (28.6%) NVP, EFV and LPV/r recipients, respectively. Mean virological-suppression (<50 copies/ml) duration was 28.6 months (median,=,22, SD,=,17.8), and only in LPV/r recipients length of suppression was associated with significantly lower HIV-RNA levels (P,=,0.015). Mean nadir CD4+ cell count of 270 cells/mm3 (median,=,240, SD,=,194.5) was significantly lower in the LPV/r arm (P,<,0.001). Nadir CD4+ level correlated with virological suppression but had opposite trends between NVP (positive) and LPV/r (negative; two tailed P,=,0.01). Logistic regression analysis showed NVP was the only independent factor associated with virologic suppression. NVP has demonstrated a distinct virological advantage at sub-clinical viral loads, possibly due to its greater penetration in extra-vascular compartments, warranting further investigation in the context of persistent low-level viraemia in long-term HAART. J. Med. Virol. 81:400,405, 2009. © 2009 Wiley-Liss, Inc. [source]

The essential oil of Croton nepetaefolius selectively blocks histamine-augmented neuronal excitability in guinea-pig celiac ganglion

JOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 8 2010
José Henrique Leal-Cardoso
Abstract Objectives,Croton nepetaefolius is a medicinal plant useful against intestinal disorders. In this study, we elucidate the effects of its essential oil (EOCN) on sympathetic neurons, with emphasis on the interaction of EOCN- and histamine-induced effects. Methods, The effects of EOCN and histamine were studied in guinea-pig celiac ganglion in vitro. Key findings, Histamine significantly altered the resting potential (Em) and the input resistance (Ri) of phasic neurons (from ,56.6 ± 1.78 mV and 88.6 ± 11.43 M,, to ,52.9 ± 1.96 mV and 108.6 ± 11.00 M,, respectively). Em, Ri and the histamine-induced alterations of these parameters were not affected by 200 µg/ml EOCN. The number of action potentials produced by a 1-s (two-times threshold) depolarising current and the current threshold (Ith) for eliciting action potentials (rheobase) were evaluated. Number of action potentials and Ith were altered by histamine (from 2.6 ± 0.43 action potentials and 105.4 ± 11.15 pA to 6.2 ± 1.16 action potentials and 67.3 ± 8.21 pA, respectively). EOCN alone did not affect number of action potentials and Ith but it fully blocked the histamine-induced modifications of number of action potentials and Ith. All the effects produced by histamine were abolished by pyrilamine. Conclusions, EOCN selectively blocked histamine-induced modulation of active membrane properties. [source]

Multiple forms of activity-dependent intrinsic plasticity in layer V cortical neurones in vivo

THE JOURNAL OF PHYSIOLOGY, Issue 13 2009
Jeanne T. Paz
Synaptic plasticity is classically considered as the neuronal substrate for learning and memory. However, activity-dependent changes in neuronal intrinsic excitability have been reported in several learning-related brain regions, suggesting that intrinsic plasticity could also participate to information storage. Compared to synaptic plasticity, there has been little exploration of the properties of induction and expression of intrinsic plasticity in an intact brain. Here, by the means of in vivo intracellular recordings in the rat we have examined how the intrinsic excitability of layer V motor cortex pyramidal neurones is altered following brief periods of repeated firing. Changes in membrane excitability were assessed by modifications in the discharge frequency versus injected current (F,I) curves. Most (,64%) conditioned neurones exhibited a long-lasting intrinsic plasticity, which was expressed either by selective changes in the current threshold or in the slope of the F,I curve, or by concomitant changes in both parameters. These modifications in the neuronal input,output relationship led to a global increase or decrease in intrinsic excitability. Passive electrical membrane properties were unaffected by the intracellular conditioning, indicating that intrinsic plasticity resulted from modifications of voltage-gated ion channels. These results demonstrate that neocortical pyramidal neurones can express in vivo a bidirectional use-dependent intrinsic plasticity, modifying their sensitivity to weak inputs and/or the gain of their input,output function. These multiple forms of experience-dependent intrinsic changes, which expand the computational abilities of individual neurones, could shape new network dynamics and thus might participate in the formation of mnemonic motor engrams. [source]

Saccadic eye movements evoked by microstimulation of striate cortex

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2003
Edward J. Tehovnik
Abstract Experiments were performed to assess the excitability of neural elements activated while inducing saccadic eye movements electrically from different cortical layers of striate cortex (area V1) in rhesus monkeys. Excitability was assessed by measuring current thresholds, saccadic latencies, chronaxies, and the effectiveness of anode-first vs. cathode-first pulses. Minimum current thresholds for the evocation of saccades (i.e. less than 5 µA) were observed when the deepest layers of V1 were stimulated. The shortest saccadic latencies were also observed at these depths. The shortest latency at 10 times the threshold current was 49 ms on average. The chronaxies of the elements mediating saccades were less in deep V1 (i.e. 0.17 ms) than in superficial V1 (i.e. 0.23 ms). Anode-first pulses were more effective at evoking saccades from superficial V1, whereas cathode-first pulses were more effective at evoking saccades from deep V1. These results indicate that the excitability properties of superficial and deep V1 are distinct for the generation of saccades. Moreover, the excitability of elements mediating saccades in V1 of monkeys is comparable to that of elements mediating phosphenes in human V1. [source]