Hot hulls might mean slipperier ships

Want to make a ship move faster through the water? Well, one thing that you can do is paint its hull with low-friction or anti-biofouling paint, to keep barnacles and other marine organisms from growing on it. According to Prof. Derek Chan, from the University of Melbourne's Department of Mathematics and Statistics, another approach that should work is to heat that hull up to a temperature of over 100C (212F). His proposed method is based on a 255 year-old principle known as the Leidenfrost effect.

Named for its discoverer, German doctor Johann Gottlob Leidenfrost, the Leidenfrost effect is the phenomenon wherein a liquid, when exposed to a solid that is significantly above that liquid's boiling point, forms an insulating vapor layer between itself and that solid. This is the reason that water droplets dance across a sufficiently-hot skillet, instead of just evaporating on the spot.

Applying that principle to a ship, Chan believes that a hull kept at an outer temperature significantly above the boiling point of water, should cause a low-friction vapor layer to form between that hull and the water. He tested the theory by analyzing high-speed footage of polished balls being dropped through liquid - their drag was reportedly greatly reduced when they were heated to the point at which the Leidenfrost effect occurred.

Not only could this be used to reduce transportation costs and greenhouse emissions from shipping, he suggests, but it could also be used to speed the flow rate of liquid through pipes.

Chan does, however, admit that keeping the hull so hot could increase the rate of corrosion, and is further researching that possibility. There is also the question of whether the energy required to heat the hull (and keep it hot, as it's exposed to cold ocean water) would be significantly less than the amount of energy that would be saved through the reduction of friction.

The University of Melbourne worked with Saudi Arabia's King Abdulla University on the research, which was recently published in the journal Physical Review Letters.

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Apple's iCloud enables automatic, wireless syncing between devices

As expected following Apple's purchase of the iCloud domain from Sweden-based Xcerion earlier this year and the construction of a US$500 million iDataCenter in Maiden, North Carolina, the company has revealed details at WWDC of exactly what its iCloud service will offer. By storing user's content in the cloud so it can be automatically pushed to various devices, iCloud will let users sync apps, media, documents, calendars and more between their various mobile iOS devices and a Mac or PC wirelessly.

iCloud, which can be turned on after upgrading to iOS 5, will provide 5GB of free storage for mail, documents, photos and backup data including device settings and app data. Thankfully, music, apps and books purchased from Apple won't count towards the 5GB, nor will the storage required for the new Photo Stream service that automatically uploads photos taken or imported on any device and wirelessly pushes them to all devices and computers. Extra storage will be also available for purchase at prices to be announced when the service goes live.

Daily iCloud backup for iOS devices will occur automatically over Wi-Fi when they are being recharged so as not to drain the device's battery or the user's mobile data quota.

With a tap of the iCloud icon, apps and books purchased from Apple on one iDevice can now be downloaded on up to 10 other iOS devices at no extra cost. Additionally, changes to documents created on iCloud compatible apps, such as Apple's iWork suite, will automatically be pushed to all the user's other devices.

iCloud also includes services previously available through MobileMe, which iCloud replaces, including calendar sharing, contacts, and an improved ad-free push Mail account hosted at me.com. In a godsend to users annoyed with the inability to simply mark message as read on iOS devices that meant needlessly opening the same messages on multiple devices, inboxes and mailboxes will now be kept up-to-date across all iOS devices and computers.

Photo Stream will automatically upload photos taken or imported on any devices to iCloud where they will be stored for 30 days so they can be wirelessly pushed to all devices and computers. Photo Stream will be built into iOS device photo apps, iPhoto on Mac, and will save images to the Picture folder on PCs. While Macs and PCs will store all photos from the Photo Stream, only the last 1,000 photos will be stored on each mobile device to save storage space.

Finally, there's iTunes in the Cloud and iTunes Match, which we already took a look at here.

While iTunes in the Cloud is available now to U.S. residents, iCloud will go live this fall (northern hemisphere) with the release of iOS 5.

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PWM : Pulse Width Modulation

The Fading example demonstrates the use of analog output (PWM) to fade an LED. It is available in the File->Sketchbook->Examples->Analog menu of the Arduino software.

Pulse Width Modulation, or PWM, is a technique for getting analog results with digital means. Digital control is used to create a square wave, a signal switched between on and off. This on-off pattern can simulate voltages in between full on (5 Volts) and off (0 Volts) by changing the portion of the time the signal spends on versus the time that the signal spends off. The duration of "on time" is called the pulse width. To get varying analog values, you change, or modulate, that pulse width. If you repeat this on-off pattern fast enough with an LED for example, the result is as if the signal is a steady voltage between 0 and 5v controlling the brightness of the LED.

In the graphic below, the green lines represent a regular time period. This duration or period is the inverse of the PWM frequency. In other words, with Arduino's PWM frequency at about 500Hz, the green lines would measure 2 milliseconds each. A call to analogWrite() is on a scale of 0 - 255, such that analogWrite(255) requests a 100% duty cycle (always on), and analogWrite(127) is a 50% duty cycle (on half the time) for example.

Once you get this example running, grab your arduino and shake it back and forth. What you are doing here is essentially mapping time across the space. To our eyes, the movement blurs each LED blink into a line. As the LED fades in and out, those little lines will grow and shrink in length. Now you are seeing the pulse width.

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