Invisibility cloak made using curved waveguides
Most researchers believe that sophisticated artificially engineered
materials are required to build an invisibility cloak. Such
“metamaterials” exhibit high losses and work for only one color. The
resulting invisibility cloaks are tiny, and cannot hide anything if
another color of light is used. Now the team of researchers from BAE
Systems, Towson University and Purdue University demonstrated a
different approach to cloaking. Instead of sophisticated metamaterials,
they use a waveguide, which is curved to mimic the metamaterial
properties. This approach leads to all-color invisibility cloak with
much lower losses. As a result, the researchers built a large optical
cloak, which is about hundred times larger than the cloaks built
previously. This “see-through” cloak bends light around itself and thus
differs from the “invisibility carpet,” which camouflages bumps on a
metal surface. The team believes that further size increase is possible,
and that the same technique may be applied to other tasks, which require
the use of metamaterials, such as building new “hyperlenses” which
considerably surpass the resolution limit of conventional lenses.
Figure: Schematic of a tapered waveguide acting as an optical cloak.
***
LB12032DR
CAN QUANTUM MECHANICS FOOL THE COSMIC CENSOR?
Summary: According to general relativity space and time loose their
meaning and the present laws of physics become useless at the
singularities hidden inside black holes. Despite it, they are harmless
because the event horizons of the holes, which "dress" them, keep
the rest of the universe protected. On the other hand, "undressed"
(i.e., naked) singularities can influence a whole region of the
universe in an unpredictable way. This "immoral behavior" led
R. Penrose to conjectured the existence of "cosmic censors" to
preclude the formation of naked singularities. Today we ignore
whether (I) "physical initial conditions evolved through Einstein
equations could generate naked singularities". This led S. Hawking,
J. Preskill and K. Thorne to run a celebrated bet, where Preskill
and Thorne favor (I) in contrast to Hawking.
In our paper, we revisit the mechanism for violating the weak
cosmic-censorship conjecture (WCCC) by overspinning a
nearly-extreme charged black hole suggested sometime ago by
some of us. The mechanism consists of an incoming massless
neutral scalar particle, with low energy and large angular
momentum, tunneling into the hole. We investigate the effect
of the large angular momentum of the incoming particle on the
background geometry and address recent claims that such a
back-reaction would invalidate the mechanism. We show that
the large angular momentum of the incident particle does not
constitute an obvious impediment to the success of the
overspinning quantum mechanism, although the induced
back-reaction turns out to be essential to restoring the validity
of the WCCC in the classical regime. These results and the fact
that quantum gravity should unveil the physics of naked
singularities and recover the predictability of the Universe
seem to endorse the view that "the cosmic censor" would be
oblivious to processes involving quantum effects. Finally, also
based on our results, we eventually raise a thought provoking
conjecture connecting naked singularities to elementary particles,
namely, that "naked singularities and elementary particles
would be low-energy manifestations of a same quantum gravity
structure" and argue that, if this is the case, the Higgs (scalar)
boson expected to be found in the LHC would be a composite
rather than an elementary particle.
***
LC12174
A "nuclear clock" could find out whether the fundamental constants of
nature are changing in time.
Laboratory searches for variation of fundamental constants, such as
the speed of light, work by comparing two or more atomic clocks over
the course of a few years. Each clock is essentially a different
physical system, with different dependence on fundamental constants.
Therefore if the speed of light (for example) changes, the two clocks
will react differently and one will seem to "speed up" relative to the
other. The discovery of changes in the constants would revolutionize
our understanding of physics, forcing us to reconsider the Standard
Model of particle physics and Einstein's General Relativity.
The setup could be massively improved by taking advantage of a
"nuclear clock" made from thorium-229. While such a clock has yet to
be built, it is expected to be the most precise clock ever made. In
this paper we have proposed experiments that can measure the
sensitivity of the clock to variation of fundamental constants. The
nuclear clock is expected to be several-orders-of-magnitude more
sensitive than atomic clocks, and hence be an excellent probe of
whether the fundamental constants of nature are changing in time.
***
LB12130
A little dirt can go a long way
It is well known that the transport of particles in a narrow channel is
slowed down considerably by the presence of other particles. this
phenomena, predicted theoretically over 30 years ago, has been
demonstrated in recent experiments on colloidal particles and in
experiments on transport in narrow biological channels. Now, scientists
at Los Alamos National Laboratory and Boston University predict that
the transport of such particles can be dramatically enhanced by addition
of very small amount disorder, which in practice can take the form of
impurities, dust, or variations in the channel width.
***
LX11566
Jet Imaging of Quark-Gluon Plasma Hints at its ¡°Yin-Yang¡± Duality
A novel energy loss pattern near the QCD confinement transition
at temperature Tc has been proposed for a jet penetrating the
quark-gluon plasma (QGP), which solves a long-standing puzzle about
the observed jet geometry. An energetic jet --- a quark or gluon with
large momentum --- loses its energy and thus makes imaging when
passing through the QGP --- the matter once occupying the early
universe and nowadays only created at laboratory by smashing heavy
nuclei head-on with a speed close to the light. In most such collisions,
the ¡°thickness¡± of the created matter is spatially anisotropic and
leads to nontrivial angular dependence of the jet energy loss --- a
geometric imaging on the ¡°opacity¡± of the QGP. In this paper, we first
pointed out the opacity of the matter has --- instead of linear growth ---
actually nonlinear dependence on the matter density and develops a peak
near Tc. Based on this, we were able to explain the measured jet
anisotropy which denied past model descriptions. The microscopic
mechanism of such novel pattern lies in the ¡°Yin-Yang¡±, or Electric-Magnetic
duality for QGP proposed in our previous paper (PRL101:162302,2008),
according to which magnetic monopoles dominate the QGP near Tc. A jet
as a moving electric charge loses substantial energy to heat up such a
magnetic plasma just like how a conduction cooker works by vertue of the
Faraday's law. These innovative ideas may eventually elucidate the
decades-old mystery of how QCD confinement transition exactly occurs
in nature.
***
EBR1046
evolution of cooperation
Our work reveals that diversity of individual rationality has great
influence on the evolution of cooperation, and the
moderate-ranked individuals are found to play a critical role. Since the
organization of society largely depends on the emergence of cooperation, our
findings might help us to understand some social phenomena, especially
concerning the middle class. In the study of evolutionary game dynamics,
most works focus on the influence of network topology and strategy
complexity, but not the diversity of individual properties. These works show
that cooperation can often be promoted while cooperators form compact
clusters. In our work, we take into concern the diversity of an
intrinsic social property, individual rationality, and discover that the
cluster forming mechanism of cooperators can either be highly enhanced or
severely deteriorated by different distributions of rationality. Slight
change in the rationality distribution may transfer the whole system from
all-cooperator state to all-defector state. Moreover, analysis of the
stability of cooperative clusters reveals the critical role played
by individuals with moderate connectivity in the evolution of the whole
system, which has not been fully discussed in former works. The inspiration
from our work might yield new insights towards the social function of the
middle class.
