LH12013

The shape of fair weather clouds

Simple descriptions of complex systems are rare. The key is to ask the
right question. For the cloud, it is the shape. Clouds have bumps.
Thermal plumes have humps. Clouds are formed by convection currents,
which also give rise to plumes. Can we understand the shape of clouds in
terms of thermal plumes ?

This simple model achieves that, starting from a simple description of
the plumes in terms of mathematical singularities (sources and sinks).
The cloud is a collection of droplets, advected by the (random) flow
field created by randomly generated plumes. Each time a plume goes
through the cloud, it leaves behind a hump in the spatial distribution
of droplets. This process dynamically generates the characteristic
“cauliflower” shape of cumulus (“fair weather”) clouds.

What’s important about this work is that it describes (quantitatively)
one specific aspect (the shape) of a complex system (the cloud) in terms
of the coherent structures in the system (the thermal plumes). Usually
one cannot do this with complex non-linear systems. In this case, this
procedure gives a simple description of a complex everyday phenomenon.


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LF12638

Designing supermarket checkouts? Ask purple bacteria

Getting customers through the door, processed, and out again as
efficiently as possible, is a primary goal for large supermarkets and
fast-food chains. But managers constantly face the major dilemma of
how many checkout lanes to have. Too many, and you leave employees
unoccupied while also sacrificing valuable floor space. Too few, and
you run the risk of large lane queues and hence losing customers. But
instead of adopting the latest market consulting fad, a new paper in
suggests taking the advice of some of the oldest
and most primitive life forms on the planet: Purple bacteria. For the
past billion years, purple bacteria -- which are all around us, from
the side of rivers to the colorful corals under the sea -- have been
solving this problem by adapting the number and arrangements of their
'checkouts' according to the flux of 'customers'. Photons from the sun
create excitations which enter the bacterial membrane like customers
through a door, wander through the nanoscale aisles (represented by
the LH2 quasi-ordered lattice) and then arrive at the nanoscale
checkouts (LH1 complex) before leaving the store (membrane) as a food
supply. Analytic theory, backed up by numerical
simulations, includes a key biological feature whose analog is well-
known to any shopper who has been stuck in a checkout lane: Each
customer (i.e. photon excitation) passing through a particular
checkout (i.e. LH1) leaves this checkout blocked for a finite time as
the bagging takes place (i.e. chemical reaction in the LH1 reaction
center). The theory shows that the interplay between
having many active checkouts (i.e. LH1s) but few lost customers (i.e.
dissipated excitations) explains why very different arrangements of
checkouts emerge under conditions of high light intensity (i.e. a high
flux of photon 'customers' arriving at the LH1 'checkouts' all the
time) and low light intensity (i.e. relatively few photon
'customers'). They are currently using their theory to fine-tune
Nature's own architectures in the hope of uncovering some super-
efficient designs for harvesting the free, renewable energy from
sunlight. So the next time your local store introduces some novel
checkout layout which manages to reduce overall checkout times, just
remember that a bacteria may have found it first -- nearly one billion
years ago.

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LG12498

A crack in a long standing ceramic problem

Ceramics are renowned for their excellent resistances to the extreme environments including high temperature and chemical corrosion, but their poor resistance to thermal shock that often occurs in the engines with ceramic components and in routine daily activities such as cooling a boiling egg in iced water has been a long standing problem in the thermal engineering. In this paper, we propose a novel method to make ceramics insensitive to thermal shock up to their melting temperature. In this method the surface of ceramics was biomimetically roughened into nano-finned surface that creates a thin air layer enveloping the surface of the ceramics during quenching. This air layer drastically increases the heat transfer resistance by about 10,000 times so that the strong thermal gradient and stresses produced by the steep temperature difference in thermal shock did not occur both on the actual surface and in the interior of the ceramics. This method effectively extends the applica
tions of existing ceramics in the extreme thermal environments.

LL12368

Optical chirality and its interaction with matter: Super-Twisty Light

Scientists have discovered a new property of light called “optical
chirality” that measures how different a light wave is from its mirror
image. They used this measure to design super-chiral electromagnetic
fields: fields that have left-right asymmetry in some regions of space
hundreds of times larger than that found in circularly polarized
light.

Ever since Louis Pasteur’s experiments on tartaric acid in 1848,
scientists have known that some molecules—called chiral
molecules—exist in distinct mirror-image forms. Electromagnetic
fields, e.g. light, can also be chiral. Circularly polarized light is
the best known chiral electromagnetic field, and is often used to
study chiral molecules. But until now, nobody asked whether some
fields could be more chiral than others, or how one would quantify the
chirality of an electromagnetic field.

The theoretical discovery of optical chirality sheds new light on the
fundamental symmetries of the electromagnetic field, and paves the way
to ultrasensitive detection and control of chiral molecules with
light.

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LN11781

Computing with a molecule

A simple diatomic molecule on the angstrom scale has executed
ultrafast Fourier transform (UFFT) within femtoseconds.
Wave functions of atoms and molecules can be used as information
carriers to replace real charges in the present Si-based circuit,
whose further integration will result in a possible disaster where
current-leakage is unavoidable with insulators thinned to atomic
levels. Furthermore, a shaped femtosecond laser pulse can access many
vibrational wave functions in a single molecule simultaneously,
encoding more than one million different kinds of information to a
simple diatomic molecule on the angstrom scale. This information
density is higher than the best possible DRAM to be developed by 2020
by two orders of magnitudes. We have experimentally demonstrated a
new logic gate based on the temporal evolution of molecular wave
functions. Optically tailored wave functions in a simple diatomic
molecule on the angstrom scale implements 4- and 8-element discrete
Fourier-transform with arbitrary real and imaginary inputs. The
evolution time is 145 femtoseconds, which is shorter than the typical
clock period of the current fastest Si-based computers by three
orders of magnitudes (the maximum clock rate of IBM Power 6 is 5.0
GHz, giving its clock period to be 200 picoseconds).

***

LL11852

NEW QUANTUM SENSOR BEATS OLD QUANTUM LIMIT

Researchers have invented an optical sensor that beats an unbeatable quantum limit to sensitivity. The breakthrough has a broad array of applications — from gravity wave observatories seeking to observe distant and bizarre astrophysical phenomena, to optical gyroscopes used in commercial navigation. Optical interferometers are some of the most sensitive devices on Earth, and they have a 100 year long history at the forefront of breakthroughs in science — from turn-of-the-century experiments measuring the speed of light (and paving the way for Einstein’s theory of relativity) — to current-day laser interferometer antennas that scan the skies for evidence of gravity waves emitted from colliding black holes. Practical applications are navigational gyroscopes found in jet planes and magnetic field sensors used in oil drills. It was thought that there was an ultimate limit on the sensitivity of such devices imposed by the laws of quantum physics. Research has now demonstrated conclusively that this limit can be broken. This work exploits quantum properties of light to design the most sensitive optical interferometer ever devised.