7,479 research outputs found
Brownian Entanglement
We show that for two classical brownian particles there exists an analog of
continuous-variable quantum entanglement: The common probability distribution
of the two coordinates and the corresponding coarse-grained velocities cannot
be prepared via mixing of any factorized distributions referring to the two
particles in separate. This is possible for particles which interacted in the
past, but do not interact in the present. Three factors are crucial for the
effect: 1) separation of time-scales of coordinate and momentum which motivates
the definition of coarse-grained velocities; 2) the resulting uncertainty
relations between the coordinate of the brownian particle and the change of its
coarse-grained velocity; 3) the fact that the coarse-grained velocity, though
pertaining to a single brownian particle, is defined on a common context of two
particles. The brownian entanglement is a consequence of a coarse-grained
description and disappears for a finer resolution of the brownian motion. We
discuss possibilities of its experimental realizations in examples of
macroscopic brownian motion.Comment: 18 pages, no figure
Schroedingers equation with gauge coupling derived from a continuity equation
We consider a statistical ensemble of particles of mass m, which can be
described by a probability density \rho and a probability current \vec{j} of
the form \rho \nabla S/m. The continuity equation for \rho and \vec{j} implies
a first differential equation for the basic variables \rho and S. We further
assume that this system may be described by a linear differential equation for
a complex state variable \chi. Using this assumptions and the simplest possible
Ansatz \chi(\rho,S) Schroedingers equation for a particle of mass m in an
external potential V(q,t) is deduced. All calculations are performed for a
single spatial dimension (variable q) Using a second Ansatz \chi(\rho,S,q,t)
which allows for an explict q,t-dependence of \chi, one obtains a generalized
Schroedinger equation with an unusual external influence described by a
time-dependent Planck constant. All other modifications of Schroeodingers
equation obtained within this Ansatz may be eliminated by means of a gauge
transformation. Thus, this second Ansatz may be considered as a generalized
gauging procedure. Finally, making a third Ansatz, which allows for an
non-unique external q,t-dependence of \chi, one obtains Schroedingers equation
with electromagnetic potentials \vec{A}, \phi in the familiar gauge coupling
form. A possible source of the non-uniqueness is pointed out.Comment: 25 pages, no figure
Additional roles of a peripheral loop–loop interaction in the Neurospora VS ribozyme
Many RNAs contain tertiary interactions that contribute to folding the RNA into its functional 3D structure. In the VS ribozyme, a tertiary loop–loop kissing interaction involving stem–loops I and V is also required to rearrange the secondary structure of stem–loop I such that nucleotides at the base of stem I, which contains the cleavage–ligation site, can adopt the conformation required for activity. In the current work, we have used mutants that constitutively adopt the catalytically permissive conformation to search for additional roles of the kissing interaction in vitro. Using mutations that disrupt or restore the kissing interaction, we find that the kissing interaction contributes ∼1000-fold enhancement to the rates of cleavage and ligation. Large Mg2+-dependent effects on equilibrium were also observed: in the presence of the kissing interaction cleavage is favored >10-fold at micromolar concentrations of Mg2+; whereas ligation is favored >10-fold at millimolar concentrations of Mg2+. In the absence of the kissing interaction cleavage exceeds ligation at all concentrations of Mg2+. These data provide evidence that the kissing interaction strongly affects the observed cleavage and ligation rate constants and the cleavage–ligation equilibrium of the ribozyme
Green Production of Anionic Surfactant Obtained from Pea Protein
A pea protein isolate was hydrolyzed by a double enzyme treatment method in order to obtain short peptide sequences used as raw materials to produce lipopeptides-based surfactants. Pea protein hydrolysates were prepared using the combination of Alcalase and Flavourzyme. The influence of the process variables was studied to optimize the proteolytic degradation to high degrees of hydrolysis. The average peptide chain lengths were obtained at 3–5 amino acid units after a hydrolysis of 30 min with the mixture of enzymes. Then, N-acylation in water, in presence of acid chloride (C12 and C16), carried out with a conversion rate of amine functions of 90%, allowed to obtain anionic surfactant mixtures (lipopeptides and sodium fatty acids). These two steps were performed in water, in continuous and did not generate any waste. This process was therefore in line with green chemistry principles. The surface activities (CMC, foaming and emulsifying properties) of these mixtures were also studied. These formulations obtained from natural renewable resources and the reactions done under environmental respect, could replace petrochemical based surfactants for some applications
Spin polarization versus lifetime effects at point contacts between superconducting niobium and normal metals
Point-contact Andreev reflection spectroscopy is used to measure the spin
polarization of metals but analysis of the spectra has encountered a number of
serious challenges, one of which is the difficulty to distinguish the effects
of spin polarization from those of the finite lifetime of Cooper pairs. We have
recently confirmed the polarization-lifetime ambiguity for Nb-Co and Nb-Cu
contacts and suggested to use Fermi surface mismatch, the normal reflection due
to the difference of Fermi wave vectors of the two electrodes, to solve this
dilemma. Here we present further experiments on contacts between
superconducting Nb and the ferromagnets Fe and Ni as well as the noble metals
Ag and Pt that support our previous results. Our data indicate that the Nb -
normal metal interfaces have a transparency of up to about 80 per cent and a
small, if not negligible, spin polarization.Comment: 7 pages, 2 figures, submitted to Proceedings of the 26th Conference
on Low Temperature Physic
Analysis of genetic systems using experimental evolution and whole-genome sequencing
The application of whole-genome sequencing to the study of microbial evolution promises to reveal the complex functional networks of mutations that underlie adaptation. A recent study of parallel evolution in populations of Escherichia coli shows how adaptation involves both functional changes to specific proteins as well as global changes in regulation
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