LL12274

A beam with an unusual stability

We report on the observation of a wave beam that does not follow the
usual laws of optics. In contrast to nearly all other wave beams, this
beam does not spread its width while propagating through a solid.
Neither reflectors nor lenses are needed to create this beam, as it
forms spontaneously when the wave is emitted by a small antenna. This
effect is not determined by the beam intensity and happens because the
wave properties depend on the propagation direction in a specific way.
In our experiments these conditions have been fashioned for spin waves,
elementary excitations of a magnetic material. We have experimentally
shown that a spin-wave beam of a width of about 0.7 mm does not broaden
itself, and remains stable over propagation distances of more than 10
mm, which is the size of the studied sample. An accompanying theoretical
prediction suggests this will hold for propagation distances more than
100-fold larger (1 m)! Due to the directivity of wave properties, these
beams do not bounce off a mirror the way light does. Instead, reflection
is governed by the application of an external magnetic field, which is
also used to steer the beam within the material.

***

LK12585

Lucky Accident Could Slash Costs of Future Fusion Power Plants

Prospects for low-cost, clean energy through nuclear fusion just got brighter, thanks to a lucky accident at Sandia National Laboratories in Albuquerque, New Mexico. For almost 40 years, research teams around the world have been pursuing energy production by tiny nuclear explosions lasting only billionths of a second within a reactor. This approach, called inertial confinement fusion or ICF, requires that tremendous power be concentrated almost instantaneously onto tiny hydrogen pellets.

Researchers had been attempting to boost the power that could be delivered to such fusion targets by fastening small cartridges to Sandia’s Saturn pulsed power generator. The cartridges worked better than hoped, doubling the generator’s current. But the researchers nearly overlooked the results, because the dramatic boost in electrical power occurred unexpectedly, only long after the Saturn generator pulse had ended. In a paper appearing in Physical Review Letters, the team theorizes that material heated off the cartridge walls blocked the current pulse, allowing electrical energy to accumulate inside the cartridge before releasing the energy suddenly into the target volume. Such a means of producing high-power pulses from low-power generators could result in savings of hundreds of millions of dollars per facility in future ICF power plants.

LK12445

Physics of Folding Two-Dimensional Lattices

Research, reported in a recently accepted Physical Review Letter,
shows a new pathway to form nanotub- like carbon nanostructures at the
edge of folded graphene. Unlike carbon nanotbes, which can be formed
with any chirality, the folded graphene predominantly are either
armchair or zigzag. To explain, the authors of the paper carried a
combined experimental and theoretical study of the physics of graphene
folding. Materials with two-dimensional (2-D) lattices, such as
graphene or single sheet of Boron nitride, can be folded under
mechanical forces in any directions. Once a 2-D lattice folds, it
creates a nanotube-like edge from the balance of the elastic stiffness
and adhesion of the lattice. However, the structure of the edge and
its stability strongly depend on the strength of adhesion between the
overlapping region, which leads to the interesting physics of folding
2-D lattices. In the work reported, the free folding of graphene was
achieved by random forces generated by ultrasound. Electron
diffraction of ~100 folded graphene offers conclusive evidence that
graphene prefers to fold either parallel or at 30 ° to the
carbon-carbon bond direction, forming the so-called armchair and
zigzag edges. Atomistic simulations show that these two folding
directions correspond to two energy minima induced by a partial or
full AB stacking of the graphene lattice. The results show that a much
better control over the atomistic structure can be obtained using the
symmetry dependence of 2-D lattice adhesion.

Caption of the figure attached: Among the 100 folded graphene we
investigated, statistically ~1/3 have armchair and ~1/3 have zigzag
folded edges. This preference was explained by the stacking of
graphene lattice from atomistic simulations.


***

LN11661

Wave-vector dependence of magnetic-turbulence spectra in the solar wind

Three-dimensional spatial structure of turbulence was determined
for the first time in space. Astrophysicists believe that turbulence
is a widespread phenomenon in the extraterrestrial world such as
stellar winds and the interstellar medium. Turbulence furthermore plays
an essential role in accretion disks and cosmic ray transport, too.
In astrophysics, gases are mostly in an ionized state, called the plasma, and
its turbulence properties are different from that of ordinary gas dynamics.
In particular, plasmas are electrically conducting and make the
ambient magnetic field fluctuate once plasmas are set into turbulent motion.
Scientists have been studying turbulence properties in situ in the
interplanetary space since 1960s, but with single spacecraft it
was not possible to distinguish between temporal oscillations and
spatial structures in the measurements.
In this paper, we use four-spacecraft measurements of the Cluster mission
and determine the three-dimensional spatial structure of turbulent
fluctuations of the interplanetary magnetic field.
We discover that turbulence develops in the plane
perpendicular to the ambient magnetic field, exhibiting
the geometry of displaced field lines without being bent.
This field line structure may be one of the fundamental properties
of astrophysical turbulence and the key of cosmic ray transport.

[Figure]
Magnetic energy distribution in the three-dimensional
wave vector domain. The energy distribution extends primarily in the direction
perpendicular to the mean magnetic field direction (denoted as B0).

***

LK12458A

Straight to the point – ultra-secure communications for specified locations

Researchers have developed a quantum communication process able to deliver unprecedented levels of security for high-sensitivity communications.

The development shows that quantum communications, which already allow unbreakable encryption, can provide an additional level of security through “unconditional location verification”.

This would ensure that, even if a secret code has fallen into the wrong hands, a secure message could only be seen by a recipient at an agreed geographic point.

With this process you can send data to a person who is at a particular location. If they are not at that location the process would detect that, and you can stop the communication.

The concept, which has potential applications in e-commerce, digital rights distribution and defence, is reported in the May edition of the American Physical Society journal Physical Review A.

It means any message or data can be received only at a particular receiver – a laptop, handset or desktop computer – at an agreed location.

The system works by sending paired qubits – particles, such as photons, which have been manipulated to contain specific quantum information – over a fibre optic or wireless network to a recipient. The recipient must send a return message, using information from the decoded qubits, to a number of reference points to open up a secure communications channel. Because quantum networks operate at the speed of light, and quantum information cannot be copied, the time to return the message can be accurately constrained, ensuring that the message has come from only one possible place.

Due to the nature of quantum mechanics, any effort to intercept the communication at a different location would be immediately detectable and, because the system is based on the laws of physics rather than computational resources, it is impossible to attack.

This is basically a new application that can be deployed on current and emerging quantum networks.

It opens up a range of new information security applications for both fibre and wireless communication networks. There are many industries and organisations – banks for example – that would be interested in delivering information content in the sure knowledge a recipient is at an agreed-upon location.

***

LK12472


Tunable Table Top Soft-X Rays for Biology and Medicine

Coherent bright soft x-ray sources are sought for the visualization
and manipulation of nanostructures and biomolecules with many
potential applications in biology and medicine. Current synchrotrons
and free-electron laser sources are large scale facilities with
limited access and therefore small table top sources available in
regular laboratories and hospitals are in high demand. High harmonic
sources are a table top alternative but currently lack in photon
yield. We report on a feasibility study to produce bright coherent
soft x-ray radiation by using DC electric fields in a tabletop high
harmonic generation device. The mechanism presented allows full
tunability in the short wavelength range of the electromagnetic
spectrum, from extreme-ultraviolet to soft-x-ray radiation thus
represents an important advance in overcoming a critical challenge in
high order harmonic generation and coherent x-ray science.