312 research outputs found
Direct transesterification of microalgae after Pulsed Electric Field ( PEF ) treatment
Background
Lipid extraction is a major bottleneck for the commercialization of microalgae due to energy costs involved during solvent recycling. Direct transesterification offers the possibility to bypass the extraction step by immediately converting the lipids to fatty acids methyl esters (FAMEs). In this study, the efficiency of direct transesterification after pulsed electric field (PEF) was evaluated. Freshly harvested Auxenochlorella protothecoides (A. protothecoides), cultivated either autotrophically or mixotrophically, was subjected to PEF. Two treatment energies were tested, 0.25 MJ/kgdw and 1.5 MJ/kgdw and results were compared with conventional two-step transesterification.
Results
For autotrophically grown A. protothecoides, the percentage of the total FAMEs recovered from untreated biomass and microalgae treated with 0.25 MJ/kgdw was 30% for both cases while for 1.5 MJ/kgdw it was 65%. A 24-h incubation step between PEF-treatment and direct transesterification significantly improved the results. Untreated biomass remained stable with 30% of FAMEs, while with both treatment energies a 97% FAME recovery was achieved. However, for mixotrophic A. protothecoides the process was not as effective. Approximately 30% of FAMEs were recovered for all three conditions immediately after PEF with only a marginal increase after incubation. The reason for this different behavior of the two cultivation modes is unknown and under investigation.
Conclusions
Overall, the synergy between PEF and direct transesterification was proven to have potential, in particular for autotrophic microalgae. Its implementation and further optimization in a biorefinery therefore merits further attention
Direct transesterification of microalgae after Pulsed Electric Field ( PEF ) treatment
Background
Lipid extraction is a major bottleneck for the commercialization of microalgae due to energy costs involved during solvent recycling. Direct transesterification offers the possibility to bypass the extraction step by immediately converting the lipids to fatty acids methyl esters (FAMEs). In this study, the efficiency of direct transesterification after pulsed electric field (PEF) was evaluated. Freshly harvested Auxenochlorella protothecoides (A. protothecoides), cultivated either autotrophically or mixotrophically, was subjected to PEF. Two treatment energies were tested, 0.25 MJ/kgdw and 1.5 MJ/kgdw and results were compared with conventional two-step transesterification.
Results
For autotrophically grown A. protothecoides, the percentage of the total FAMEs recovered from untreated biomass and microalgae treated with 0.25 MJ/kgdw was 30% for both cases while for 1.5 MJ/kgdw it was 65%. A 24-h incubation step between PEF-treatment and direct transesterification significantly improved the results. Untreated biomass remained stable with 30% of FAMEs, while with both treatment energies a 97% FAME recovery was achieved. However, for mixotrophic A. protothecoides the process was not as effective. Approximately 30% of FAMEs were recovered for all three conditions immediately after PEF with only a marginal increase after incubation. The reason for this different behavior of the two cultivation modes is unknown and under investigation.
Conclusions
Overall, the synergy between PEF and direct transesterification was proven to have potential, in particular for autotrophic microalgae. Its implementation and further optimization in a biorefinery therefore merits further attention
Structural Insight into Eukaryotic Sterol Transport through Niemann-Pick Type C Proteins
Niemann-Pick type C (NPC) proteins are essential for sterol homeostasis, believed to drive sterol integration into the lysosomal membrane before redistribution to other cellular membranes. Here, using a combination of crystallography, cryo-electron microscopy, and biochemical and in vivo studies on the Saccharomyces cerevisiae NPC system (NCR1 and NPC2), we present a framework for sterol membrane integration. Sterols are transferred between hydrophobic pockets of vacuolar NPC2 and membrane-protein NCR1. NCR1 has its N-terminal domain (NTD) positioned to deliver a sterol to a tunnel connecting NTD to the luminal membrane leaflet 50 Å away. A sterol is caught inside this tunnel during transport, and a proton-relay network of charged residues in the transmembrane region is linked to this tunnel supporting a proton-driven transport mechanism. We propose a model for sterol integration that clarifies the role of NPC proteins in this essential eukaryotic pathway and that rationalizes mutations in patients with Niemann-Pick disease type C
Incubation time after pulsed electric field treatment of microalgae enhances the efficiency of extraction processes and enables the reduction of specific treatment energy
High precision measurement of the associated strangeness production in proton proton interactions
A new high precision measurement of the reaction pp -> pK+Lambda at a beam
momentum of 2.95 GeV/c with more than 200,000 analyzed events allows a detailed
analysis of differential observables and their inter-dependencies. Correlations
of the angular distributions with momenta are examined. The invariant mass
distributions are compared for different regions in the Dalitz plots. The cusp
structure at the N Sigma threshold is described with the Flatt\'e formalism and
its variation in the Dalitz plot is analyzed.Comment: accepted for publication in Eur. Phys. J.
First Model-Independent Measurement of the Spin Triplet Scattering Length from Final State Interaction in the Reaction
The reaction has been measured with the
COSY-TOF detector at a beam momentum of . The polarized
proton beam enables the measurement of the beam analyzing power by the
asymmetry of the produced kaon (). This observable allows the
spin triplet scattering length to be extracted for the first time
model independently from the final-state interaction in the reaction. The
obtained value is . This value is
compatible with theoretical predictions and results from model-dependent
analyses.Comment: Revised version as accepted for publication in PR
Low-Energy \Lambda-\p Scattering Parameters from the Reaction
Constraints on the spin-averaged scattering length and effective
range have been obtained from measurements of the reaction
close to the production threshold by comparing model phase-space Dalitz plot
occupations with experimental ones. The data fix well the position of the
virtual bound state in the system. Combining this with information
from elastic scattering measurements at slightly higher energies,
together with the fact that the hyperdeuteron is not bound, leads to a new
determination of the low energy scattering parameters.Comment: 18 pages, 7 figure
Non-equilibrium emission of complex fragments from p+Au collisions at 2.5 GeV proton beam energy
Energy and angular dependence of double differential cross sections
d/ddE was measured for reactions induced by 2.5 GeV protons
on Au target with isotopic identification of light products (H, He, Li, Be, and
B) and with elemental identification of heavier intermediate mass fragments (C,
N, O, F, Ne, Na, Mg, and Al). It was found that two different reaction
mechanisms give comparable contributions to the cross sections. The
intranuclear cascade of nucleon-nucleon collisions followed by evaporation from
an equilibrated residuum describes low energy part of the energy distributions
whereas another reaction mechanism is responsible for high energy part of the
spectra of composite particles. Phenomenological model description of the
differential cross sections by isotropic emission from two moving sources led
to a very good description of all measured data. Values of the extracted
parameters of the emitting sources are compatible with the hypothesis claiming
that the high energy particles emerge from pre-equilibrium processes consisting
in a breakup of the target into three groups of nucleons; small, fast and hot
fireball of 8 nucleons, and two larger, excited prefragments, which
emits the light charged particles and intermediate mass fragments. The smaller
of them contains 20 nucleons and moves with velocity larger than the CM
velocity of the proton projectile and the target. The heavier prefragment
behaves similarly as the heavy residuum of the intranuclear cascade of
nucleon-nucleon collisions. %The mass and charge dependence of the total
production cross %sections was extracted from the above analysis for all
observed %reaction products. This dependence follows the power low behavior
%(A or Z)
Kaon Production and Interaction
Exclusive data on both the elementary kaon and antikaon production channels
have been taken at the cooler synchrotron COSY in proton-proton scattering. In
the kaon--hyperon production an enhancement by one order of magnitude of the
Lambda/Sigma0 ratio has been observed at excess energies below Q=13 MeV
compared to data at higher excess energies (Q>300 MeV). New results obtained at
the COSY-11 facility explore the transition region between the regime of this
low-energy Sigma0 suppression and excess energies of 60 MeV. A comparison of
the energy dependence of the Lambda and Sigma0 total cross sections exhibits
distinct qualitative differences between both hyperon production channels.
Studies of kaon-antikaon production have been motivated especially by the
ongoing discussion about the nature of the scalar resonances f0(980) and
a0(980) coupling to the K anti-K channel. For the reaction pp->ppK+K- a first
total cross section value is reported at an excess energy of Q=17 MeV, i.e.
below the phi threshold. Calculations obtained within an OBE model indicate
that the energy dependence of the available total cross section data close to
threshold is rather difficult to reconcile with the assumption of a phase-space
behaviour modified predominantly by the proton-proton final state interaction.Comment: 10 pages, 4 figures, Presented at Meson 2002: 7th International
Workshop on Meson Production, Properties and Interaction, Cracow, Poland,
24-28 May 200
The Near-Threshold Production of Phi Mesons in pp Collisions
The pp->pp phi reaction has been studied at the Cooler Synchrotron
COSY-Juelich, using the internal beam and ANKE facility. Total cross sections
have been determined at three excess energies epsilon near the production
threshold. The differential cross section closest to threshold at epsilon=18.5
MeV exhibits a clear S-wave dominance as well as a noticeable effect due to the
proton-proton final state interaction. Taken together with data for pp
omega-production, a significant enhancement of the phi/omega ratio of a factor
8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.Comment: 4 Pages, 3 Figures, 1 Table, submitted to Phys. Rev. Let
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