RELIABLE DETECTION OF SIGNAL TONES IN PRESENCE OF COLLISIONS

A reliable and energy-efficient contention resolution mechanism (CRM) is a crucial component of MAC protocols for wireless sensor networks (WSNs). Among a number of CRM proposals, CRMs based on exchanging short signal tones between competing nodes have recently drawn attention due to their promise of collision-freedom and energy-efficiency. However, the basic assumption of these protocols, i.e. the possibility to reliably detect the presence/absence of signal tone in case of simultaneous transmissions from multiple nodes, has not yet been confirmed. In this paper we present a technique for signal tone generation/detection, which uses only standard features of off-the-shelf RF transmitters. Furthermore, we present results of an experimental validation carried out in a real testbed which demonstrate a high accuracy of signal tone detection in presence of multiple simultaneous transmissions.

The role of Ca2+-activated Cl− current in tone generation in the rabbit corpus cavernosum

Rabbit corpus cavernosum smooth muscle (RCCSM) cells express ion channels that produce Ca2+-activated Cl− ( IClCa) current, but low sensitivity to conventional antagonists has made its role in tone generation difficult to evaluate. We have reexamined this question using two new generation IClCa blockers, T16Ainh-A01 and CaCCinh-A01. Isolated RCCSM cells were studied using the perforated patch method. Current-voltage protocols revealed that both L-type Ca2+ current and IClCa. T16Ainh-A01 and CaCCinh-A01 (10 μM) reduced IClCa by ~85%, while 30 μM abolished it. L-type Ca2+ current was unaffected by 10 μM CaCCinh-A01 but was reduced by 50% at 30 μM CaCCinh-A01, 46% at 10 μM T16Ainh-A01, and 78% at 30 μM T16Ainh-A01. Both drugs reduced spontaneous isometric tension in RCCSM strips, by 60–70% at 10 μM and >90% at 30 μM. Phenylephrine (PE)-enhanced tension was also reduced (ED50 = 3 μM, CaCCinh-A01; 14 μM, T16Ainh-A01). CaCCinh-A01 at 10 μM had little effect on 60 mM KCl contractures, though they were reduced by 30 μM CaCCinh-A01 and T16Ainh-A01 (10 μM and 30 μM) consistent with their effects on L-type Ca2+ current. Both drugs also reversed the stimulatory effect of PE on intracellular Ca2+ waves, studied with laser scanning confocal microscopy in isolated RCCSM cells. In conclusion, although both drugs were effective blockers of IClCa, the effect of T16Ainh-A01 on L-type Ca2+ current precludes its use for evaluating the role of IClCa in tone generation. However, 10 μM CaCCinh-A01 selectively blocked IClCa versus L-type Ca2+ current and reduced spontaneous and PE-induced tone, suggesting that IClCa is important in maintaining penile detumescence.

Flow-Induced Noise of Perforated Plates at Oblique Angles of Incidence

This paper investigates experimentally the mechanism of tone generation from flow over a simplified model of a perforated plate. To simplify the geometry to two dimensions, a perforated plate is modeled by a series of rectangular slats with an adjustable gap width between them. This apparatus is tested at various angles of incidence and flow velocities, to identify the conditions favorable to the production of tonal noise. The results of this research are presented in two main parts. First, the acoustic response of the test plates is documented by means of microphone measurements. It is found that for an angle of incidence between 5 and 30 degrees and a flow velocity of 10 to 30 m/s, tonal noise is produced. Outside of this range of angles, the produced sound is broadband. In the second part, phase-locked particle image velocimetry (PIV) is used to study the flow field. It is found that vortices form in the free shear layer of the gaps between the slats. These vortices impinge on the side of the downstream slat and are then ejected through the gap to the backside of the plate. As these vortices leave the edge of the downstream slat, counter rotating vortices are shed in sympathy with the incident vortices. Vortex pairs are therefore periodically shed which are thought to be the cause of tone generation.