Minimum-risk path finding by an adaptive amoebal network
The plasmodium of the primitive organism, the giant amoeba Physarum,
is able to find the minimum-risk path in a spatially inhomogeneous
field of risk.
Thus the amoeba has the capacity for information processing in
optimizing its physiological requirements.
When two food-sources are presented to the plasmodium in the dark,
a thick tube for absorbing nutrients is formed that connects the food-
sources through the shortest route.
When the light-avoiding organism is partially illuminated,
however, the tube connecting the food-sources follows a different route.
Defining risk as the experimentally measurable rate of light-avoiding
movement,
the minimum-risk path is exhibited by the organism, determined by
integrating along the path.
We note that the evolution of the tube network shares features in
common with Hebbian learning
found in neuronal networks, as the tubes grow or shrink and disappear
based on their level of activity.
***
A BIOPHYSICAL THEORY FOR ACTION-AT-A-DISTANCE IN THE BRAIN
Brain-imaging studies have shown that---during directed mental tasks
and also during resting wakefulness---separated regions of the cortex
"light up" to generate waves of synchronized electrical activity.
But what causes these different brain centres to become active
simultaneously?
In this paper [1], we propose that this "action at a distance" co-
ordination of neuron behavior arises naturally from the gap-junction
connections that couple the neurons and glia (neuron support cells)
within the central nervous system. These electrical synapses are
found in all mammalian cells. In the brain, they provide a direct
electrical connection allowing fast inter-neuron communications that
supplement the well-studied primary communication channel involving
chemical synapses driven by action potential "spikes."
Our theory suggests that---provided electrical diffusion via gap-
junctions is sufficiently strong---the brain will spontaneously
organize into distinct regions of high- and low-firing activity that
will exchange contrast on slow time-scales. These spatial patterns
are called Turing structures, named for mathematician Alan Turing,
who, in 1952, first demonstrated that competing diffusion reactions
could explain pattern-formation in biology. The figure below shows a
sample of the range of Turing patterns generated by our cortical model.
***
Colloidal traffic-control on a magnetic lab-on-a-chip
If you have ever worried about times to commute from one place to another
in a big city you will appreciate a smart traffic system. Pietro Tierno,
Tom Johansen and Thomas Fischer from the Florida State University and the
University of Oslo have designed a smart magnetic traffic control for small
particles on a lab on the chip that might be used as fast drug delivery
system. A magnetic field rotating with a frequency slightly faster than the
particles on the lab-onthe-chip can follow significantly reduces their time
of commuting through array of magnetic domains.
49eaefd9.jpg
***
With a second dimension of time, 2T-physics appears to give a better
description of the natural world.
Evidence has been accumulating that the ordinary formulation of physics
(1T physics) is insufficient to describe certain aspects of our world,
just like shadows on walls alone are insufficient to capture the true
essence of an object in a three dimensional room. According to Two-Time
Physics (2T physics), there is more to space-time than what can be
garnered with 1T physics.
The Standard Model of Particles and Forces (SM), which captures all the
physical realities that are experimentally confirmed up to now, happens
to be a particular 3+1 dimensional shadow of a 2T-physics field theory
in 4+2 dimensions, as shown last year. Among the successes of the
2T-physics approach to the Standard Model is the resolution of the
strong CP problem of QCD without an elusive axion.
To help grasp the relation between 1T-physics and 2T physics, consider
the many possible shadows of a 3 dimensional object projected from
different perspectives on the surrounding walls of a 3-dimensional room.
Just like a flatlander, that can crawl and measure only on the surface
of the wall, would think that the shadows of different shapes are
different "beasts" and move differently, so does 1T-physics presents
different dynamical systems in terms of different Hamiltonians, although
according to 2T-physics these apparently different systems are clearly
related to each other since there is a unique dynamical system in 4+2
dimensions that generates all of the 1-time "shadows". Thus 2T-physics
provides a new kind of unification.
So 2T-physics claims that there are other "shadows" of the 4+2 version
of the Standard Model that have different interpretations from the point
of view of 1T-physics in 3+1 dimensions. A program for studying these
"duals" of the Standard Model has been launched recently in a separate
paper (arXiv:0705.2834, accepted for publication in Phys. Rev.)
In this letter the formulation of the general supersymmetric version of
2T-physics field theory in 4 + 2 dimensions is outlined, for fields of
spins 0, 1/2 , 1, with N = 1 supersymmetry (SUSY). This will be a
starting point for physical applications in the form of the
supersymmetric version of the SM in 4 + 2 dimensions. Due to symmetry
constraints that arise through the 4+2 higher spacetime, it is
conceivable that there will be measurable consequences that can
distinguish 2T-physics from other approaches in experiments at the Large
Hadron Collider at CERN that will begin to produce new data in 2008.
For more information see links at my homepage:
http://physics1.usc.edu/~bars/
***
A twist in the search for the Higgs boson
The emergence of the Higgs boson decay mode into two pseudoscalar
bosons, which can relieve the so-called little hierarchy problem and
reduce the LEP2 Higgs boson mass bound, may affect the golden search
modes (h -> gamma gamma, b b-bar) of the Higgs boson significantly.
The LHC may not be able to find the Higgs boson if the
two-pseudoscalar decay mode dominates. Our Letter explicitly shows
that the associated production of the Higgs boson with a W or Z boson
can recover the loss of sensitivity in the golden modes. With the
Higgs boson decaying into two pseudoscalar bosons, which further decay
into 4 b jets, together with at least a charged lepton from the W or Z
boson decay, a significant Higgs boson signal is observable at the
LHC. The ultimate goal of the LHC is hunt for the Higgs boson, which
is responsible for electroweak symmetry breaking and mass generation.
***
The new structure of mother-of-pearl
Biominerals are of interest to material scientists, physicists,
chemists and engineers because of their remarkable mechanical
properties and their fascinatingly complex, self-assembled architecture.
Biominerals, including mollusk and crustacean shells, bone, teeth and
eggshell, are composites of micro-crystals and organics. Metzler et
al. (PRL, accepted for publication) discovered that the orientation
of each micro-crystal in the nacre (or mother-of-pearl) layer inside
red abalone shells can be revealed by imaging nacre with synchrotron
spectromicroscopy. With this high-resolution and sensitivity
microscopy approach the micro-crystals composing nacre stand out, and
their relative orientations are revealed by different gray-levels.
The contrast arises from a mechanism called x-ray linear dichroism,
discovered by Joachim Stöhr (J. Stöhr et al., Phys. Rev. Lett. 47,
381 (1981)), now director of the Stanford Synchrotron Radiation
Laboratory. Linear dichroism has been widely used to study man-made
structures, including superconductors and magnetic materials, but
this is the first discovery of such mechanism in a natural, biogenic
material.
The experiments were conducted at the University of Wisconsin
Synchrotron Radiation Center, where the principal investigator in
this work, Prof. Pupa Gilbert, of UW-Physics, led a group since she
joined UW in 1999. She also served as Scientific Director at the SRC
from 2002 to 2006.
The new dichroic contrast mechanism revealed individual stacks of co-
oriented tablets, and how these are packed in situ, in pristine
nacre. Comparing previous data and their new data, Gilbert and
physics graduate student Rebecca A. Metzler, in collaboration with
theorist Prof. Susan N. Coppersmith, also at UW-Physics, found that
the data are most consistent with a specific model for nacre
formation: randomly distributed nucleation sites are pre-formed in
organic matrix layers, and tablet n+1 nucleation and growth only
starts when the underlying tablet n has reached its final height.
More experiments, currently underway, will make all observations
quantitative. More theoretical models, in three dimensions, will
further refine the nacre formation mechanism, which has puzzled the
scientific community for decades.
