Line-of-Sight Pursuit in Monotone and Scallop Polygons

We study a turn-based game in a simply connected polygonal environment [Formula: see text] between a pursuer [Formula: see text] and an adversarial evader [Formula: see text]. Both players can move in a straight line to any point within unit distance during their turn. The pursuer [Formula: see text] wins by capturing the evader, meaning that their distance satisfies [Formula: see text], while the evader wins by eluding capture forever. Both players have a map of the environment, but they have different sensing capabilities. The evader [Formula: see text] always knows the location of [Formula: see text]. Meanwhile, [Formula: see text] only has line-of-sight visibility: [Formula: see text] observes the evader’s position only when the line segment connecting them lies entirely within the polygon. Therefore [Formula: see text] must search for [Formula: see text] when the evader is hidden from view. We provide a winning strategy for [Formula: see text] in two families of polygons: monotone polygons and scallop polygons. In both families, a straight line [Formula: see text] can be moved continuously over [Formula: see text] so that (1) [Formula: see text] is a line segment and (2) every point on the boundary [Formula: see text] is swept exactly once. These are both subfamilies of strictly sweepable polygons. The sweeping motion for a monotone polygon is a single translation, and the sweeping motion for a scallop polygon is a single rotation. Our algorithms use rook’s strategy during its pursuit phase, rather than the well-known lion’s strategy. The rook’s strategy is crucial for obtaining a capture time that is linear in the area of [Formula: see text]. For both monotone and scallop polygons, our algorithm has a capture time of [Formula: see text], where [Formula: see text] is the number of polygon vertices.

Impact of Sweeping Jet on Area-Averaged Impingement Heat Transfer

A series of sweeping jet-impingement experiments are conducted over a circular heated surface, with a main objective of understanding the impact of the unique flow field on the resulting heat transfer. The sweeping motion of the fluidic oscillator is influenced by the sweeping frequency and sweeping angle where each is directly dependent on the geometric design (i.e. internal feedback loops, mixing chamber, etc.). The target surface consists of a heated copper disk, where heater power is supplied to the bottom surface of the disk and adjusted until a differential of 30°C is obtained between the jet and target surface temperatures. An energy balance over the target surface temperatures provides a means for calculating area-averaged heat transfer rate, hence Nusselt number. An increase in the sweeping jet’s thermal inertia initiates an augmentation in heat transfer due to sweeping motion of the jet across the target surface. PIV data was acquired for two jet configurations, confined and unconfined, so that the recirculation behavior can be determined. The fluidic oscillator is found to improve only at a low z/d. At large z/d (greater than 4 in this study), the fluidic oscillator adversely affects the heat transfer.

Torsional Tip Motion of Double Beam Atomic Force Microscopy

This paper investigates the vibration of a coupled microcantilever beam structure, in which a rigid body at their free end connects the two beams. The coupled beams are under equal and out-of-phase forces applied by piezoelectric films, which result in overall torsional motion. The equations describing the motion of the structure as well as the boundary conditions are developed using the Hamilton principle under the assumption of the structure being an Euler-Bernoulli beam. Two equations for each beam are realized: bending and torsional equations, which are combined in one torsional equation. The equation is solved using Galerkin approximation. The effects of dimensional parameters and input parameters are investigated including height, width, thickness, beam arrangement, applied voltage, input frequency, and mass of the tip. Geometry and mass were found to have significant effects on the angle, while input voltage was found to have a small linear effect. The overall sweeping motion was found to have an angle well below one degree in general. This shows that while the piezoelectric actuators can generate torsional sweeping, the effect is at a small angle that depends more on design than actuation force.

Developing and testing a computer vision method to quantify 3D movements of bottom-set gillnets on the seabed

Gillnets are one of the most widely used fishing gears, but there is limited knowledge about their habitat effects, partly due to the lack of methodology to quantify such effects. A stereo imaging method was identified and adapted to quantify the dynamic behaviour of gillnets in-situ. Two cameras took synchronized images of the gear from slightly different perspectives, allowing to estimate the distance from the observation unit to the gear such as in the human 3D vision. The sweeping motion on the seabed and the penetration into the sediment of the leadline of light and heavy commercial bottom gillnets deployed in sandy habitats in the Danish coastal plaice fishery were assessed. The direct physical disruption of the seabed was minimal as the leadline was not penetrating into the seabed. Direct damage to the benthos could however originate from the sweeping movements of the nets, which were found to be higher than usually estimated by experts, up to about 2 m. The sweeping movements were for the most part in the order of magnitude of 10 cm, and resulted in a total swept area per fishing operation lower than any of the hourly swept area estimated for active fishing gears. Whereas the general perception is that heavy gears are more destructive to the habitat, light nets were moving significantly more than heavy ones. The established methodology could be further applied to assess gear dynamic behaviour in situ of other static gears.

Space–time pressure–velocity correlations in a turbulent boundary layer

The spatio-temporal pressure–velocity correlation in a turbulent boundary layer is investigated so as to understand the link between pressure fluctuations and turbulent coherent structures. A new experimental set-up is developed to measure the pressure fluctuations at the wall and in the field and, simultaneously, the velocity field by stereoscopic particle image velocimetry. The present measurement area covers the whole boundary layer thickness, and the spatial resolution of the measurement is good enough to assess the representative length scales of the flow. The Reynolds number effect is quantified from the data at $\mathit{Re}_{{\it\theta}}=7300$, 10 000, 18 000. The spatio-temporal three-dimensional structures of the pressure–velocity correlations, $\boldsymbol{R}_{pu}$, $\boldsymbol{R}_{pv}$ and $\boldsymbol{R}_{pw}$, are evaluated. The wall pressure fluctuations are closely coupled with coherent structures which occupy a large region of the boundary layer in the wall-normal and spanwise directions and up to $10{\it\delta}/U_{e}$ in time, where ${\it\delta}$ and $U_{e}$ denote the boundary layer thickness and the free stream velocity. Reynolds number effects are mainly observed on the size and intensity of the pressure–velocity correlations. Conditioning the correlations on the pressure signal sign shows different types of flow phenomena linked to the positive and negative pressure events. For the wall pressure, positive pressure fluctuations appear to be correlated with the leading edge of a large sweeping motion of splatting type followed by a large ejection. The negative pressure fluctuations are linked to a localized ejection upstream, followed by a large sweeping motion downstream. For the pressure fluctuations in the field, in addition to the structures observed with the wall pressure, the pressure–velocity correlations exhibit a significant correlation in a region very extended in time. Such long structures appear to be independent of the one observed at the wall and to grow significantly in time with the Reynolds number when scaling with external variables. When conditioned by the pressure sign, clear ejection and sweeping motions are observed with associated streamwise vortical structures at a scale of the order of $0.2{\it\delta}$. These structures can be linked to the large-scale motion and very-large-scale motion previously observed by different authors and seem to organize in a scheme analogous to the near-wall cycle, but at a much larger scale.

The Local Anaesthetic Effect of a Dental Laser Prior to Cavity Preparation: A Pilot Volunteer Study

SUMMARY Objectives It has been suggested that laser preconditioning can produce dental anaesthesia. This study aimed to assess the response of the dental pulp to laser preconditioning. Methods The effects of laser preconditioning, sham laser (negative control), and composite curing light (positive control) on the response of the dental pulp to electric pulp testing was investigated in this double-blind crossover trial with six volunteers. The Er,Cr:YSGG laser or curing light was shone on a premolar tooth in a sweeping motion for 30 seconds (in the sham treatment, the laser was not activated) in blindfolded volunteers subjected to a consistent aural stimulus. Treatment method at each visit was randomized and performed by a researcher not involved in pulp testing. Teeth were pulp tested twice initially by another member of the research team to get baseline readings, immediately following the treatment, and thereafter every two minutes for 10 minutes. Results were analyzed using analysis of variance and an independent-sample t-test. Results There were no significant differences in pulpal response between treatments (p>0.05). Conclusion Laser preconditioning did not affect pulpal response as measured by an electronic pulp tester. Laser preconditioning did not result in any pain or noticeable symptoms for both teeth and soft tissues.

Atmospheric TIG Arc Diagnostics with a Low Disturbance Electrostatic Probe

The use of electrostatic probe is available and simple in atmospheric TIG arc plasma diagnostic. Usually electrostatic probe takes disturbance in arc plasma due to sweeping motion. A low disturbance electrostatic probe was developed. This probe consisted of aluminum wire and moved through arc plasma along probe’s longitudinal direction to avoid sweeping motion. And the signal collected by this probe required Abel inversion to convert into the value per 1 mm probe length. With the application of the low disturbance probe in biased condition, ion saturation current density in various sections along the axial direction of TIG arc was obtained. The result shows that half width and peak value of ion saturation current density increase with the enhance of arc current; the radius of current-carrying area can be estimated by the half width of ion saturation current density; along the axial direction of TIG arc, the radius of current-carrying area change to the minimum near cathode.