top of page


Public·10 members


If a particular channel has a high bounce rate, take a look at your marketing efforts for that channel: for example, if users coming via display are bouncing, make sure your ads are relevant to your site content.


Engineering surfaces that promote rapid drop detachment1,2 is of importance to a wide range of applications including anti-icing3,4,5, dropwise condensation6 and self-cleaning7,8,9. Here we show how superhydrophobic surfaces patterned with lattices of submillimetre-scale posts decorated with nanotextures can generate a counter-intuitive bouncing regime: drops spread on impact and then leave the surface in a flattened, pancake shape without retracting. This allows a fourfold reduction in contact time compared with conventional complete rebound 1,10,11,12,13. We demonstrate that the pancake bouncing results from the rectification of capillary energy stored in the penetrated liquid into upward motion adequate to lift the drop. Moreover, the timescales for lateral drop spreading over the surface and for vertical motion must be comparable. In particular, by designing surfaces with tapered micro/nanotextures that behave as harmonic springs, the timescales become independent of the impact velocity, allowing the occurrence of pancake bouncing and rapid drop detachment over a wide range of impact velocities.

Figure 1b shows selected snapshots of a drop impinging on such a surface at We = 7.1. On touching the surface at t = 0, part of the drop penetrates into the post arrays in a localized region with the radius approximately equivalent to the initial drop radius and recoils back, driven by the capillary force, to the top of the surface at 2.9 ms (Supplementary Movie 1). After reaching a maximum lateral extension19 at 4.8 ms, the drop retracts on the surface and finally detaches from the surface at 16.5 ms (). This contact time is in good agreement with previous results for conventional complete rebound 1,10,11,12. However, at higher We, the drop exhibits a distinctively different bouncing behaviour, which we term pancake bouncing, as exemplified by an impact at We = 14.1 (Fig. 1c and Supplementary Movie 2). In this case, the liquid penetration is deeper and the drop detaches from the surface (at 3.4 ms ) immediately after the capillary emptying without experiencing retraction.

We also performed drop impact experiments on tilted surfaces, a geometry more relevant to practical applications, such as self-cleaning7,8,9, de-icing 3,4,5 and thermal management6,20. Figure 1d shows selected snapshots of a drop impinging on the tapered surface with a tilt angle of 30 at We = 31.2 (Supplementary Movie 3, left). The drop impinging on the tilted tapered surface also exhibits pancake bouncing. Moreover, the drop completely detaches from the surface within 3.6 ms and leaves the field of view without bouncing again. We also compared the drop impact on the tilted surface with nanoflower structure alone. The apparent contact angle of the nanostructured surface is 160 1.8. It is evident that a drop impinging on such a surface follows a conventional bouncing pathway: the drop spreads to a maximum diameter, recoils back, and finally leaves the surface within 14.5 ms (Fig. 1e and Supplementary Movie 3, right).

To pin down the key surface features and drop parameters for the occurrence of pancake bouncing, we plotted the variation of k with in the design diagram (Fig. 4). Filled symbols represent pancake bouncing (defined by Q > 0.8) and open symbols denote conventional bouncing. Region 1 corresponds to the pancake bouncing occurring on straight posts with 1.0

Recent health system shocks such as the Ebola disease outbreak have focused global health attention on the notion of resilient health systems. In this commentary, we reflect on the current framing of the concept of resilience in health systems discourse and propose a reframing. Specifically, we propose that: (1) in addition to sudden shocks, health systems face the ongoing strain of multiple factors. Health systems need the capacity to continue to deliver services of good quality and respond effectively to wider health challenges. We call this capacity everyday resilience; (2) health system resilience entails more than bouncing back from shock. In complex adaptive systems (CAS), resilience emerges from a combination of absorptive, adaptive and transformative strategies; (3) nurturing the resilience of health systems requires understanding health systems as comprising not only hardware elements (such as finances and infrastructure), but also software elements (such as leadership capacity, power relations, values and appropriate organizational culture). We also reflect on current criticisms of the concept of resilient health systems, such as that it assumes that systems are apolitical, ignoring actor agency, promoting inaction, and requiring that we accept and embrace vulnerability, rather than strive for stronger and more responsive systems. We observe that these criticisms are warranted to the extent that they refer to notions of resilience that are mismatched with the reality of health systems as CAS. We argue that the observed weaknesses of resilience thinking can be addressed by reframing and applying a resilience lens that is better suited to the attributes of health systems as CAS.

A bouncing bomb is a bomb designed to bounce to a target across water in a calculated manner to avoid obstacles such as torpedo nets, and to allow both the bomb's speed on arrival at the target and the timing of its detonation to be pre-determined, in a similar fashion to a regular naval depth charge.[Fn 1] The inventor of the first such bomb was the British engineer Barnes Wallis, whose "Upkeep" bouncing bomb was used in the RAF's Operation Chastise of May 1943 to bounce into German dams and explode under water, with effect similar to the underground detonation of the Grand Slam and Tallboy earthquake bombs, both of which he also invented.

It was under such circumstances that Upkeep came to be deployed independently of Highball. In addition to continuing problems in testing Highball, it had been observed at the end of March 1943 that "At best [aircrews] would need two months' special training".[35] With this in mind, 618 Squadron had been formed on 1 April 1943 at RAF Skitten, near Wick, in northeastern Scotland, to undertake "Operation Servant", in which Tirpitz would be attacked with Highball bouncing bombs.[36] On 18 April it was recommended that Operation Servant should be undertaken before the end of June, since 618 Squadron could not be held back for this purpose indefinitely. It was not until early September 1943 that, in view of continuing problems with both Highball and its release mechanism, most of 618 Squadron was "released for other duties". This in practice meant the abandonment of Operation Servant.[37] Core personnel of 618 Squadron were retained and these continued work on the development of Highball.[38]

In 2011, a project led by Dr Hugh Hunt of the Department of Engineering, University of Cambridge, re-created the bouncing bomb and tested it in a Dambusters-like raid. Buffalo Airways was selected as the company to fly the mission with their Douglas DC-4. The project was documented in the documentary television show Dambusters Fly Again in Canada and Australia, Dambusters: Building the Bouncing Bomb in the UK, and the Nova episode Bombing Hitler's Dams in the US. It involved dropping a replica dummy bomb, which performed as intended, striking a replica dam which had been specially constructed; this was subsequently destroyed by a charge placed where the bomb had landed.[52][53][54][55][56][excessive citations] The filming of the documentary was itself documented as part of the Ice Pilots NWT reality television series that follows Buffalo Airways in season 3 episode 2 "Dambusters".[57]

A truly cyclic universe would circumvent these problems: If the universe is engaged in endless cycles of expansion and contraction, it need not have a beginning at all. But as Kinney notes, these bouncing models raise their own array of untenable questions.

The concept of bouncing seems to be one of the most misunderstood and confusing terms for beginners in music production. It seems like every DAW calls this something else, and every DAW has a different way of doing it. Below I have included some frequently asked questions regarding the topic:

A bouncing ball model is an example of a hybrid dynamic system. A hybrid dynamic system is a system that involves both continuous dynamics and discrete transitions where the system dynamics can change and the state values can jump. The continuous dynamics of a bouncing ball is given by these equations:

The sldemo_bounce_two_integrators model uses two Integrator blocks to model a bouncing ball. The Integrator block on the left is the velocity integrator modeling the first equation. The Integrator block on the right is the position integrator. Open the position integrator block dialog box and observe that the block has a lower limit of zero. This condition represents the constraint that the ball cannot go below the ground.

The sldemo_bounce model uses a single Second-Order Integrator block to model a bouncing ball. In this case, the second equation is internal to the Second-Order Integrator block in this case. Open the Second-Order Integrator block dialog box and see that has a lower limit of zero. On the Attributes tab, check Reinitialize dx/dt when x reaches saturation. This parameter allows you to reinitialize ( in the bouncing ball model) to a new value when reaches its saturation limit. So, in the bouncing ball model, when the ball hits the ground, its velocity can be set to a different value, such as to the velocity after the impact. Note the loop for calculating the velocity after a collision with the ground. To capture the velocity of the ball just before the collision, the output port of the Second-Order Integrator block and a Memory block are used. is then used to calculate the rebound velocity .

  • About

    Welcome to the group! You can connect with other members, ge...

    bottom of page