Login with your Social Account

Blueberry pancake

Researchers explain the unique movement of Pancake when swirled

When a glass filled with wine is swirled clockwise, the wine will also spin in the clockwise direction, however, while making a blueberry pancake, if it is swirled in the clockwise direction, the pancake spins in an anticlockwise direction.

The same is the case with a glass of beads. A few beads will rotate clockwise when the glass is swirled clockwise. However, a lot of beads in a glass when swirled clockwise will rotate counterclockwise.

Lisa Lee, a graduate student of Applied Physics at School of Engineering and Applied Sciences, Harvard said she was surprised at the behaviour of these exact same objects under the same situations.

The research team set about to understand the physics behind these actions and it turns out that friction is responsible for this. Beads are a part of a class of material called granular media, which means a collection of macroscopic particles such as sand or snow. The work appears in the Physical Review E journal.

Wine rotates clockwise when moved clockwise due to wine being a liquid-like granular media in low friction, while pancakes rotate in an anticlockwise direction when rotated clockwise which is similar to granular media under high friction.

Macroscopic particles are very interesting as they can move like a liquid or a solid depending on the conditions. Sand flows like a liquid in an hourglass but acts like a solid to support your weight on beaches. The object transition from liquid to solid has been an open question for decades.

Lee and the researchers found out that smaller groups of beads will have lower effective friction than larger pairs of beads which results in the transition from liquid to solid. When one particle rolls in one direction it experiences little friction however if many particles which are in contact with each other roll in the same direction, then they experience a large amount of friction which causes the group to solidify and thus change the behavior.

Using computer simulations, Lee and co-authors, John Paul Ryan and Miranda Holmes-Cerfon showed that in the absence of friction, the particles never solidified, no matter the quantity in which they were present. The rougher the particles were, the quicker was the transition from liquid to solid.

Shmuel Rubinstein, Associate Professor of Applied Physics at SEAS and senior author of the study said that this is an interesting case of system-size behaviors emerging from local interactions. The emergence of coherent circulations is an exciting subject for study like the case of 2D turbulence and active spinners. It is quite interesting that daily objects such as marbles and dishes can demonstrate similar physics.

Journal Reference: Physical Review E.

Insulator 4 Layers Heat Shield

Scientists manufacture 10 atoms thick heat shield to protect electronic devices

  • Stanford researchers demonstrated layers of materials having a thickness of just a few atoms stacked like paper sheets on top of the hot spots provide equivalent insulation to that of a 100 times thicker glass sheet.
  • Researchers used a graphene layer and three other materials having a thickness of three atoms for creating an insulator of four layers which has a thickness of 10 atoms.
  • The heat shield is very effective as on passing through each layer, atomic heat vibrations due to electrons-atom collisions are dampened, thereby losing energy.

These days smartphones, laptops come with a ton of features. Companies are making them more attractive with powerful enhancements both in design and technology. These come with a cost. In this case, devices get heated up quickly which if not controlled can lead to malfunctions and even explosion of devices.

To protect against these issues, scientists insert objects such as glass, plastic or even air layers for the purpose of insulation so that the components which generate heat such as microprocessors are prevented from damage and therefore make the use of the devices comfortable.

Researchers from the Stanford University have demonstrated that layers of materials having a thickness of just a few atoms which are stacked like paper sheets on top of the hot spots can provide equivalent insulation to that of a glass sheet that is 100 times thicker. In the near future, comparatively thinner heat shields will help in making electronic devices even more compact. The paper has been published in the journal Science Advances. Eric Pop, an electrical engineering professor said that now heat generated in electronic devices are being treated in a completely different fashion.

The heat generated from laptops or smartphones is in fact an inaudible form of sound having a high frequency. Electricity flows as the stream of electrons move through wires. In their motion, they collide with the atoms of the medium in which they are moving. With every collision, atoms of the medium vibrate and as the collisions increase the vibrations in the material generate energy which is felt as heat.

Viewing heat as a form of sound inspired scientists to draw upon principles of the physical world. Pop from his earlier stint as a radio DJ knew that recording studios are quiet due to the thick glass windows which block any external sound. This also applies to the present electronic devices. To make electronic devices thinner researchers borrowed the trick of homeowners who installed windows with air gaps between glass sheets with varying thickness to make homes quiet and warm. Sam Vaziri, lead author said that they similarly made an insulator which used several layers of material with a thickness of an atom instead of a thick glass sheet.

The atomically thin materials were only discovered 15 years ago. The first material was graphene comprising of one layer of carbon atoms. After that, researchers experimented with other materials that resembled a sheet. Researchers from Stanford used a graphene layer and three other materials having a thickness of three atoms for creating an insulator of four layers which has a thickness of 10 atoms. It is effective as on passing through each layer, atomic heat vibrations are weakened thereby losing energy.

For making these heat shields practical, scientists will have to find some technique by which they are easily produced. In the future, researchers wish to control vibrational energy inside materials similar to light and electricity. A new field of phononics is rising for understanding heat in solids as a type of sound.

Journal Ref: Ultrahigh thermal isolation across heterogeneously layered two-dimensional materials