13,515 research outputs found
Bioproduction of L-piperazic acid in gram scale using Aureobasidium melanogenum
Currently, piperazic acid is chemically synthesized using ecologically unfriendly processes. Microbial synthesis from glucose is an attractive alternative to chemical synthesis. In this study, we report the production of L-piperazic acid via microbial fermentation with the first engineered fungal strain of Aureobasidium melanogenum; this strain was constructed by chassis development, genetic element reconstitution and optimization, synthetic rewiring and constitutive genetic circuit reconstitution, to build a robust L-piperazic acid synthetic cascade. These genetic modifications enable A. melanogenum to directly convert glucose to L-piperazic acid without relying on the use of either chemically synthesized precursors or harsh conditions. This bio-based process overcomes the shortcomings of the conventional synthesis routes. The ultimately engineered strain is a very high-efficient cell factory that can excrete 1.12 ± 0.05 g l-1 of L-piperazic acid after a 120-h 10.0-l fed-batch fermentation; this is the highest titre of L-piperazic acid reported using a microbial cell factory
Adaptive fuzzy control for a marine vessel with time-varying constraints
An adaptive fuzzy neural network (FNN) control scheme is proposed for a marine vessel with time-varying constraints, guaranteed transient response and unknown dynamics. A series of continuous constraint functions are introduced to shape the motion of a marine vessel. To deal with the constraint problems and transient response problems, an asymmetric time-varying barrier Lyapunov function is designed to ensure that the system states are upper bounded by the considered constraint functions. FNNs are constructed to identify the unknown dynamics. Considering existing approximation errors when FNNs approximating the unknown dynamics, an adaptive term is designed to compensate the approximation errors in order to obtain accurate control. Via Lyapunov stability theory, it has been proved that all the states in the closed-loop system are uniformly bounded ultimately without violating the corresponding prescribed constraint region. Two comparative simulations are carried out to verify the effectiveness of the proposed control
Spin constrained orbital angular momentum control in high-harmonic generation
The interplay between spin and orbital angular momentum in the up-conversion
process allows us to control the macroscopic wave front of high harmonics by
manipulating the microscopic polarizations of the driving field. We demonstrate
control of orbital angular momentum in high harmonic generation from both solid
and gas phase targets using the selection rules of spin angular momentum. The
gas phase harmonics extend the control of angular momentum to
extreme-ultraviolet wavelength. We also propose a bi-color scheme to produce
spectrally separated extreme-ultraviolet radiation carrying orbital angular
momentum
Spectroscopic study of blue compact galaxies V. oxygen abundance and the metallicity-luminosity relation
This is the fifth paper in a series studying the stellar components, star
formation histories, star formation rates and metallicities of a blue compact
galaxy (BCG) sample. Based on our high-quality ground-based spectroscopic
observations, we have determined the electron temperatures, electron densities,
nitrogen abundances and oxygen abundances for 72 star-forming BCGs in our
sample, using different oxygen abundance indicators. The oxygen abundance
covers the range 7.15 < 12 + log (O/H)< 9.0, and nitrogen is found to be mostly
a product of secondary nucleosynthesis for 12 + log (O/H)>8.2 and apparently a
product of primary nucleosynthesis for 12 + log (O/H)< 8.2. To assess the
possible systematic differences among different oxygen abundance indicators, we
have compared oxygen abundances of BCGs obtained with the Te method, R23
method, P method, N2 method and O3N2 method. The oxygen abundances derived from
the Te method are systematically lower by 0.1-0.25 dex than those derived from
the strong line empirical abundance indicators, consistent with previous
studies based on region samples. We confirm the existence of the
metallicity-luminosity relation in BCGs over a large range of abundances and
luminosities. Our sample of galaxies shows that the slope of the
metallicity-luminosity relation for the luminous galaxies (~-0.05) is slightly
shallower than that for the dwarf galaxies (~-0.17). An offset was found in the
metallicity-luminosity relation of the local galaxies and that of the
intermediate redshift galaxies. It shows that the metallicity-luminosity
relation for the emission line galaxies at high redshift is displaced to lower
abundances, higher luminosities, or both.Comment: 11 pages, 4 figure
The Indirect Search for Dark Matter with IceCube
We revisit the prospects for IceCube and similar kilometer-scale telescopes
to detect neutrinos produced by the annihilation of weakly interacting massive
dark matter particles (WIMPs) in the Sun. We emphasize that the astrophysics of
the problem is understood; models can be observed or, alternatively, ruled out.
In searching for a WIMP with spin-independent interactions with ordinary
matter, IceCube is only competitive with direct detection experiments if the
WIMP mass is sufficiently large. For spin-dependent interactions IceCube
already has improved the best limits on spin-dependent WIMP cross sections by
two orders of magnitude. This is largely due to the fact that models with
significant spin-dependent couplings to protons are the least constrained and,
at the same time, the most promising because of the efficient capture of WIMPs
in the Sun. We identify models where dark matter particles are beyond the reach
of any planned direct detection experiments while being within reach of
neutrino telescopes. In summary, we find that, even when contemplating recent
direct detection results, neutrino telescopes have the opportunity to play an
important as well as complementary role in the search for particle dark matter.Comment: 17 pages, 10 figures, published in the New Journal of Physics 11
105019 http://www.iop.org/EJ/abstract/1367-2630/11/10/105019, new version
submitted to correct Abstract in origina
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