How cargo can be transported in the cell, forward or backward?
It is very important for the cell to transport products and rubbish out of it and take raw materials and nutrition into it. It is well known that almost all these works are done by the cooperation of different molecular motors. But why these cargos can be transported in certain direction?. In my recent research, this enigmatic story is partly unclosed. The initial numbers of different molecular motors which bind to the moving track determines the direction of the cargo movement. I believe this theoretical result will be demonstrated experimentally in the future.
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LH11208E
Genomes at the Edge of Chaos
Even to experts, genomes, or genomic sequences, look far more like scrambled
texts than the Books of Life they are. In this paper we use a new quantity,
the order index, to measure the randomness -- or order -- of sequences to
show genomes are characteristically at the "edge of chaos" and thereby gain
insight on how genomes grew. The order index, denoted by the Greek letter
phi, maps sequences of descending order (or increasing randomness) to a phi
ranging from 1 to 0. The phi of a random sequence of length L (in bases) is
proportional to the reciprocal of the root of L; phi becomes zero only when
the length approaches infinity. Phi decreases exponentially with the number
of random mutations per site a sequence suffers, and an ordered sequence
about 1 million to 1 billion bases long -- range of typical genome length --
becomes random after it suffers about four mutations per site. We find that
the phi’s of complete genomes congregate in a small range within a factor of
two of 0.03. This means that genomes, regardless of their true lengths, are
as random as an ordered sequence becomes after it has suffered 1.5 to 2.1
mutations per site; hence the edge-of-chaos metaphor. Our simulations of
genome growth based on random segmental duplications suggest that the
universal value 0.03 represents a "fixed-point" that is a property of the
dynamics of a robust and stochastic process of genome growth and evolution.
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ACR1026
Flux-Equipped Quantum Cloak makes Ideal Matter-Wave Interferometer
Harry Potter’s invisibility cloak that can hide an object from being detected by
electromagnetic waves and is externally invisible has been proved feasible in recent
studies. An interesting generalization of such a Sci-fi tool in the quantum territory
that hides an object from matter waves has also been proposed.
In this paper, we explore the quantum interference effect of matter waves caused by a
magnetic flux hidden in the cloaked region. We show that although the quantum cloak
perfectly guides the charged matter waves detouring the cloaking shell, the global
quantum interference effect (the Aharonov-Bohm effect) is inevitable just like in the
non-cloaked case.
According to our results, the flux-equipped quantum cloak not only provides an ideal
setup to cloak an object from the detection of matter waves but also is an ideal matter-
wave interferometer that helps to reveal the global interferences of charged matter
waves. Similar ideas may be developed in the future to help manifesting other
mysterious global quantum interference effects such as the AB-EPR effect, Aharonov-
Casher effect, and so forth.
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LA12210
Traffic jams in the cell: lost in translation
The process by which proteins are made in the cell is called translation. In this process, huge molecular machines, called ribosomes, translate a sequence of nucleotides -a messenger RNA molecule- into a sequence of amino acids -a protein. This process can be modelled by particles in a lattice that hop from one site to the next with a certain probability. Each site of the lattice has associated a different hopping probability, since at eachsi of the mRNA molecule, the ribosome has to wait on average a different time interval to get the appropriate amino acid. Therefore, if one ribosome has to wait a long time at a certain site, a queue of ribosomes can form behind, leading to a traffic j.
In this paper, we have studied how the configuration of slow sites influences the current of particles on the lattice, or equivalently, the current of ribosomes on the mRNA molecule. We have shown that depending where the slow sites of the lattice are positioned, the current of particles can be subject to a first order phase transition. We have analysed 500 mRNA sequences from yeast and found that we can classify them into two main groups, depending whether they experience a phase transition or not. Most importantly, these two groups of mRNA molecules translate into proteins with two very distinct biological functions. Therefore, our theory predicts a clascation of mRNA sequences purely based on the dynamics of the ribosome trac, and we have shown that this classcation matches perfectly the biological function, providing thus the link between the phase transition and biological function.
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ET10332
Water harvesting using a conducting polymer
Currently, the most important environmental issue is the global climate
change. The significance of climate change extends, however, beyond being
the reason for some of the phenomena that are occuring in Nature, as it
also provides a new framework for recognizing the severity of a whole host
of other problems. One such problem is water scarcity. A recent report by
a United Nations panel on climate change stated that there is water
shortage for 1.1 - 3.2 billion people around the world. Such dire warnings
have given rise to the research field of water harvesting, which is
focused on developing new methods of harvesting water from various
sources. One such source is the atmosphere that has many advantages over
other sources, such as the purity of its water. It is estimated that there
are as much as 50,000 km^3 of water in the atmosphere at any given time.
We have been studying, both experimentally and by molecular dynamics
simulations, the possibility of using doped polyaniline (PANI), a conducting
polymer, as a water adsorbent by measuring the amount of water vapor that is
adsorbed on the PANI, when it is exposed to water-vapor containing air.
Due to ionic solvation, PANI absorbs large amounts of water. While there are
many polymers that absorb a significant amount of water, they do not
desorb it readily. But, by passing a very weak current through PANI, the water
is recovered. Our study indicates promise for the method, particularly for
arid and isolated areas.
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LC12857ER
Chemo-motion
We reveal a new structure caused by interaction between the reaction-
diffusion process and a surface-tension-driven effect with motor-like
surface motion via chemo-mechanical transduction. Recently, increasing
attention has been focused on the self-organized pattern formation in
nonlinear complex systems far from equilibrium. The ideal reaction-
diffusion systems have been extensively investigated to understand the
mechanism of pattern formation. For example, the excitable Belousov–
Zhabotinsky (BZ) reaction coupled with diffusion can exhibit a large
variety of spatial patterns. On other hand, chemically driven
convection can lead to a complex hydrodynamic phenomena spontaneously
induced by spiral waves. In this paper, we report on superimposed
spiral structures that are chemical spiral waves and a rotating global
structure with motor-like surface motion, providing evidence of a
hierarchical self-organized order that connects two complex phenomena
involving the coupling of a reaction–diffusion pattern with
convection. Thus, chemo-mechanical transduction in a reaction-
diffusion-convection system offers wide flexibility for designing a
hierarchical structure in nonlinear systems far from equilibrium.
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BX10924
Copper oxide reshaped
Just like carbon changes its properties under extreme pressures to form
diamond, copper oxide can be morphed into a different crystal structure
by using thin film epitaxial stabilization. When copper oxide is
deposited onto single crystal SrTiO3, under the right conditions a more
symmetric crystal structure is formed, which resembles its form found in
High Tc cuprate superconductors. Natural CuO (tenorite) is the
exceptional member of the rock salt series as one traverses the periodic
table from MnO to CuO. It deviates substantially from the trends
exhibited by the members with lower atomic number. All the others have
the cubic rock salt structure and all are correlated antiferromagnetic
insulators. The properties of CuO in higher symmetry structures would be
of great fundamental interest in understanding correlated materials. The
results demonstrate that higher symmetry phases of this important
correlated oxide are possible and now available for physical studies. If
such a high-J CuO could be doped, its properties would be of great
interest in the context of the earlier mentioned high-Tc
superconductors.
***
LY11510
Discovery of Unusually Shaped Combustion Particles May Lead to
Nano-Engineering of Particle Properties
Nanoparticles emitted by high-temperature combustion are formed through aggregation of small spheres into complex shapes. These shapes previously have been found to be uniformly open structured (—a characteristic that affects Earth’s radiation balance, climate, visibility, and human health. A multi-institutional team led by Rajan Chakrabarty and Hans Moosmüller from the Desert Research Institute (DRI) reports for the first time that some aggregates from a premixed flame have different, much more linear shapes. Electric fields in flames orient some aggregates and make some individual spheres move preferentially along electric field lines, resulting in aggregates with a more linear shape. This effect may be enhanced further by application of an external electric field, opening the door to nano-engineering of aggregate shape. Applications of this novel nano-engineering technique include industrial production of nanomaterials including carbon black, titania, and silica nanoparticles, allowing for control of shape-dependent material properties such as the blackness of carbon black particles.
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LX11459
Exotic relativistic effects of particles moving at ultra-slow speeds
Relativistic effects are well known to occur at the speeds of particles close to that of light. Can you image that relativistic effects may also be present for particles moving at ultra-slow speeds? In this paper, a relativistic Dirac-like equation is established for ultra-cold atoms moving at speeds around a centimeter per second, a magnitude of 10 orders less than the speed of light in vacuum. It is shown that particles described by the Dirac-like equation can be massless, just like photons. Remarkably, these massless particles are entirely delocalized in disordered one-dimensional systems due to a so-called chiral symmetry, in sharp contrast to a famous conventional wisdom on Anderson localization: any disorder leads to the localization of all non-relativistic electrons in one-dimensional systems. It is also elaborated how to detect experimentally the predicted relativistic effects with the current technology available for ultra-cold atoms.
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LD12562
How to Make the Smallest Atoms
Researchers have shown how to create and observe atoms a hundred times
smaller than those that make up ordinary matter. Instead of being
composed of electrons, protons, and neutrons, these atoms are made from
muons, short-lived particles that are frequently created in nature when
cosmic rays strike the earth's upper atmosphere. Nevertheless, the same
electric and magnetic fields that hold together ordinary atoms also make
these "true muonium" atoms possible. The tiny atoms decay after only
some trillionths of a second, but the researchers have uncovered
unambiguous methods by which the signature of their formation and decay
can be readily detected in particle accelerators. In one method, the
electron and positron beams intersect at a sharp angle, creating true
muonium atoms that are not only thrown clear of the clutter of beam
particles, but at relativistic speeds that greatly enhance their
lifetimes, making them easier to detect. In the other method, the
electron and positron beams collide in the traditional head-on manner,
but the true muonium atom is created alongside an extra photon against
which it recoils, again kicking it out of the beam clutter; such
processes can occur even at today's existing accelerators. In either
case, state-of-the-art laser techniques can be used to study the true
muonium atoms in detail.
***
LT11375AR
Probing quantum chaos with an atom interferometer
Coherence and interference are fundamental properties of quantum mechanical
systems that cause quantum dynamics to be different from classical dynamics.
With the advent of the atomic quantum kicked rotor, the quantum equivalent of a
classically chaotic delta kicked rotor system, it has been possible to probe
striking quantum features and to study a boundary between classical and quantum
dynamics in a single system. One of the most intriguing features of such system
are sharp peaks in the energy spectra, known as quantum resonances and quantum
accelerator modes, which occur when the period of perturbation equals the
characteristic times of a quantum system. Previous studies of quantum kicked
rotor that measure only the energy had low resolution that limits experimental
exploration of all the predicted phenomena. In our work, we demonstrate a
matter-wave interferometry scheme with cold atoms in which landmark features of
the quantum kicked rotor are produced and directly probed by momentum coherences
with high contrast. Our observations indicate that quantum resonances preserve
the matter-wave coherence rather than destroy it. High resolution of the atom
interferometer allows us to explore fundamental fractional effects of the
quantum kicked rotor and develop new atom-optics-based sensors.
