836 research outputs found
Screening of microbial communities associated with endive lettuce during postharvest processing on industrial scale
In this study, the composition of the microbial community on endive lettuce (Cichorium endivia) was evaluated during different postharvest processing steps. Microbial community structure was characterized by culture-dependent and culture-independent methods. Endive lettuce was sampled exemplarily at four different stages of processing (raw material, cut endive lettuce, washed endive lettuce, and spin-dried (ready to pack) endive lettuce) and analysed by plate count analysis using non-selective and selective agar plates with subsequent identification of bacteria colonies by matrix-assisted laser desorption/ionization time-of light mass spectrometry (MALDI-TOF MS). Additionally, terminal-restriction fragment length polymorphism (TRFLP) analysis and 16S rRNA gene nucleotide sequence analysis were conducted. The results revealed structural differences in the lettuce microbiomes during the different processing steps. The most predominant bacteria on endive lettuce were detected by almost all methods. Bacterial species belonging to the families Pseudomonadaceae, Enterobacteriaceae, Xanthomonadaceae, and Moraxellaceae were detected in most of the examined samples including some unexpected potentially human pathogenic bacteria, especially those with the potential to build resistance to antibiotics (e.g., Stenotrophomonas maltophilia (0.9 % in cut sample, 0.4 % in spin-dried sample), Acinetobacter sp. (0.6 % in raw material, 0.9 % in cut sample, 0.9 % in washed sample, 0.4 % in spin-dried sample), Morganella morganii (0.2 % in cut sample, 3 % in washed sample)) revealing the potential health risk for consumers. However, more seldom occurring bacterial species were detected in varying range by the different methods. In conclusion, the applied methods allow the determination of the microbiome's structure and its dynamic changes during postharvest processing in detail. Such a combined approach enables the implementation of tailored control strategies including hygienic design, innovative decontamination techniques, and appropriate storage conditions for improved product safety
Superconductivity in hole-doped C60 from electronic correlations
We derive a model for the highest occupied molecular orbital band of a C60
crystal which includes on-site electron-electron interactions. The form of the
interactions are based on the icosahedral symmetry of the C60 molecule together
with a perturbative treatment of an isolated C60 molecule. Using this model we
do a mean-field calculation in two dimensions on the [100] surface of the
crystal. Due to the multi-band nature we find that electron-electron
interactions can have a profound effect on the density of states as a function
of doping. The doping dependence of the transition temperature can then be
qualitatively different from that expected from simple BCS theory based on the
density of states from band structure calculations
Recommended from our members
Sublethal injury and Viable but Non-culturable (VBNC) state in microorganisms during preservation of food and biological materials by non-thermal processes
The viable but non-culturable (VBNC) state, as well as sublethal injury of microorganisms pose a distinct threat to food safety, as the use of traditional, culture-based microbiological analyses might lead to an underestimation or a misinterpretation of the product's microbial status and recovery phenomena of microorganisms may occur. For thermal treatments, a large amount of data and experience is available and processes are designed accordingly. In case of innovative inactivation treatments, however, there are still several open points with relevance for the investigation of inactivation mechanisms as well as for the application and validation of the preservation processes. Thus, this paper presents a comprehensive compilation of non-thermal preservation technologies, i.e., high hydrostatic pressure (HHP), pulsed electric fields (PEFs), pulsed light (PL), and ultraviolet (UV) radiation, as well as cold plasma (CP) treatments. The basic technological principles and the cellular and molecular mechanisms of action are described. Based on this, appropriate analytical methods are outlined, i.e., direct viable count, staining, and molecular biological methods, in order to enable the differentiation between viable and dead cells, as well as the possible occurrence of an intermediate state. Finally, further research needs are outlined
Asymmetric Squares as Standing Waves in Rayleigh-Benard Convection
Possibility of asymmetric square convection is investigated numerically using
a few mode Lorenz-like model for thermal convection in Boussinesq fluids
confined between two stress free and conducting flat boundaries. For relatively
large value of Rayleigh number, the stationary rolls become unstable and
asymmetric squares appear as standing waves at the onset of secondary
instability. Asymmetric squares, two dimensional rolls and again asymmetric
squares with their corners shifted by half a wavelength form a stable limit
cycle.Comment: 8 pages, 7 figure
The influence of Galactic aberration on precession parameters determined from VLBI observations
The influence of proper motions of sources due to Galactic aberration on
precession models based on VLBI data is determined. Comparisons of the linear
trends in the coordinates of the celestial pole obtained with and without
taking into account Galactic aberration indicate that this effect can reach 20
as per century, which is important for modern precession models. It is
also shown that correcting for Galactic aberration influences the derived
parameters of low-frequency nutation terms. It is therefore necessary to
correct for Galactic aberration in the reduction of modern astrometric
observations
Screening, Coulomb pseudopotential, and superconductivity in alkali-doped Fullerenes
We study the static screening in a Hubbard-like model using quantum Monte
Carlo. We find that the random phase approximation is surprisingly accurate
almost up to the Mott transition. We argue that in alkali-doped Fullerenes the
Coulomb pseudopotential is not very much reduced by retardation
effects. Therefore efficient screening is important in reducing
sufficiently to allow for an electron-phonon driven superconductivity. In this
way the Fullerides differ from the conventional picture, where retardation
effects play a major role in reducing the electron-electron repulsion.Comment: 4 pages RevTeX with 2 eps figures, additional material available at
http://www.mpi-stuttgart.mpg.de/docs/ANDERSEN/fullerene
Mott Transition in Degenerate Hubbard Models: Application to Doped Fullerenes
The Mott-Hubbard transition is studied for a Hubbard model with orbital
degeneracy N, using a diffusion Monte-Carlo method. Based on general arguments,
we conjecture that the Mott-Hubbard transition takes place for U/W \propto
\sqrt{N}, where U is the Coulomb interaction and W is the band width. This is
supported by exact diagonalization and Monte-Carlo calculations. Realistic
parameters for the doped fullerenes lead to the conclusion that stoichiometric
A_3 C_60 (A=K, Rb) are near the Mott-Hubbard transition, in a correlated
metallic state.Comment: 4 pages, revtex, 1 eps figure included, to be published in Phys.Rev.B
Rapid Com
VLBI measurement of the secular aberration drift
While analyzing decades of very long baseline interferometry (VLBI) data, we
detected the secular aberration drift of the extragalatic radio source proper
motions caused by the rotation of the Solar System barycenter around the
Galactic center. Our results agree with the predicted estimate to be 4-6 micro
arcseconds per year ({\mu}as/yr) towards {\alpha} = 266\circ and {\delta} =
-29\circ. In addition, we tried to detect the quadrupole systematics of the
velocity field. The analysis method consisted of three steps. First, we
analyzed geodetic and astrometric VLBI data to produce radio source coordinate
time series. Second, we fitted proper motions of 555 sources with long
observational histories over the period 1990-2010 to their respective
coordinate time series. Finally, we fitted vector spherical harmonic components
of degrees 1 and 2 to the proper motion field. Within the error bars, the
magnitude and the direction of the dipole component agree with predictions. The
dipole vector has an amplitude of 6.4 \pm 1.5 {\mu}as/yr and is directed
towards equatorial coordinates {\alpha} = 263\circ and {\delta} = -20\circ. The
quadrupole component has not been detected. The primordial gravitational wave
density, integrated over a range of frequencies less than 10-9 Hz, has a limit
of 0.0042 h-2 where h is the normalized Hubble constant is H0/(100 km s-1)
- …