Loops, leafs, and optimal transport networks
In this paper we show that the optimal architecture of a transport network that is subject to random damage or fluctuations in the load is not the simple tree-like architecture of networks optimized for efficiency. Instead, it contains intricate, hierarchical loops that obviate the ordered branching from top to bottom level. The intricate architecture of the loops allows the flow to be optimally redirected in response to disruptions, and might confer a strong evolutionary advantage to the organisms that adopt it.
Leaf venation is a pervasive example of an organism endowed with a complex biological transport network. Dicotyledon leaf venation in particular has a large number of functional, nested, closed loops.
Damage, as would be imposed on a leaf by an insect of herbivore, or fluctuations in the load, as observed in the leaf stomatal openings when the leaf is under conditions of stress, might be the driving force behind
the reticulate, elaborate venation patterns that we are so familiar with.
***
LH12229DR
The Holographic Universe
In the paper "Holography for Cosmology" we develop a holographic theory for the very early Universe,
the epoch when the seeds for the structure we see in today's Universe (the stars and galaxies)
were first created. The holographic principle, suggested by 't Hooft and Susskind in the
early nineties, states that our Universe resembles a hologram:
everything in the Universe, even the laws of physics themselves, may be reconstructed from
a theory living in only two space and one time dimensions. This theory contains forces
such as the electromagnetic and nuclear forces, but not gravity. Examples
of how this might work have been developed in string theory over the
last ten years. In this paper, we show how the very early Universe may be described holographically.
The holographic framework we develop automatically incorporates the conventional theory - inflation -
which proposes that the early Universe underwent a brief period of accelerated expansion.
However, our holographic framework also reveals completely new theories that only
have a holographic description and were thus invisible to previous approaches.
We show that these new theories are consistent with current observations, yet their predictions
are nonetheless different from standard inflation allowing for a 'smoking gun'-type detection.
Over the next few years, new observations from the Planck satellite and other experiments are expected to
pinpoint the precise value of many cosmological parameters: the results might well provide the first direct
observational evidence for the holographic nature of our Universe.
***
LM12444
All correlations, one theory
Entanglement, a quantum correlation, is called by some to be the
resource that allows faster computing, better measurements, and secure
communication. Others have argued in favor of other quantum
correlations for such enhancements, like quantum discord, an
information theoretic measure of 'quantumness' of correlations. In
this paper, we develop a method to quantify different correlations as
distances. Our method allows us encompass entanglement, quantum
discord, and classical correlations under a single umbrella theory and
is applicable for arbitrary number of particles. We further go on to
construct an new quantity, called quantum dissonance, which similar to
quantum discord but excludes entanglement. We found in our studies,
that many of these correlations added to give other correlations,
called additivity properties. All of these facts put together, our
theory will allow physicists to study and compare different
correlations for a variety of experiments and applications.
***
AJ10498
Atmospheric turbulence can be useful for global quantum
communication
The reliability of modern secure communication, including electronic
payment or secure network protocols, is based on the ambiguous
supposition that some mathematical problems cannot be resolved in a
reasonable time. The situation can be successfully improved by the
methods of quantum cryptography, which provides a physical defence
for sending confidential information. A problem is that such
methods, which are usually based on quantum light, appear to be
highly fragile. With increasing losses in the transmission channels
the chance for a successful realization of quantum protocols quickly
diminishes.
In a recent experiment the group of A. Zeilinger has demonstrated
that light may preserve its quantum properties even after
propagation through extremely lossy atmospheric channels [Nature
Physics 5, 389 (2009)]. We have theoretically analyzed this
interesting situation and obtained a clear interpretation of the
experiments. Due to the turbulence phenomena, the atmosphere
temporarily appears to be very transparent. The used measurement
techniques just choose such events and discard the data recorded
with really high losses. This knowledge may play an important role
for designing systems for purposes of global quantum communication
based on satellites.
***
LH12061
Neutral but not indifferent: When net neutral bodies behave like charged
ones
That likes repel and opposites attract is a statement that does not seem
to hold only for
electrostatics but has found its way from physics into broader aspects
of life as well.
In the past several years it has become clear though, that in the case
of strongly charged
bodies likes can attract and opposites repel! This constitutes a major
shift in paradigm
in colloidal and soft matter science in general and has allowed us to
get a deeper
understanding of complicated phenomena like DNA collapse. We now show
that there
can be long-range interactions even between net neutral objects if they
carry small
amounts of positive and negative charges, randomly frozen within their
body or on their
surface. The physical basis of this effect is that even though a frozen
charge in the system
on the average feels no net charge from other charges, it feels its
image charges and is thus
either attracted to or repelled from its image charges. This long-range
interaction stands
at odds with the commonly accepted view that neutral objects can
interact only via
multipolar or van der Waals forces and could have major implications in
other fields
such as colloidal science. Our paper shows that a disorder induced
long-range
attraction between net neutral bodies may even swamp the ubiquitous
Casimir force
under certain circumstances. Indeed, such an additional attractive
force has recently
been inferred from experimental observations and our work may help
disentangle
disorder effects from the real Casimir effect.
