Actinobacillus succinogenes is a promising bacterial catalyst for the bioproduction of succinic acid from low-cost raw materials. In this work, a genome-scale metabolic model was reconstructed and ...used to assess the metabolic capabilities of this microorganism under producing conditions.
The model, iBP722, was reconstructed based on the functional reannotation of the complete genome sequence of A. succinogenes 130Z and manual inspection of metabolic pathways, covering 1072 enzymatic reactions associated with 722 metabolic genes that involve 713 metabolites. The highly curated model was effective in capturing the growth of A. succinogenes on various carbon sources, as well as the SA production under various growth conditions with fair agreement between experimental and predicted data. Calculated flux distributions under different conditions show that a number of metabolic pathways are affected by the activity of some metabolic enzymes at key nodes in metabolism, including the transport mechanism of carbon sources and the ability to fix carbon dioxide.
The established genome-scale metabolic model can be used for model-driven strain design and medium alteration to improve succinic acid yields.
The GESPECOR software was extended to incorporate procedures for the computation of the efficiency transfer factor for cases of practical interest: (a) sources with identical geometry, but different ...matrices; (b) sources with similar (but not identical) geometry; and (c) transfer from a point source to a volume source. Fast and accurate algorithms, based on correlated sampling, were implemented for solving the first two cases. A procedure to take into account the imperfect charge collection in the detector was implemented.
The second part of an intercomparison of the coincidence summing correction methods is presented. This exercise concerned three volume sources, filled with liquid radioactive solution. The same ...experimental spectra, decay scheme and photon emission intensities were used by all the participants. The results were expressed as coincidence summing corrective factors for several energies of 152Eu and 134Cs, and different source-to-detector distances. They are presented and discussed.
Context.The detection of radio pulses from cosmic ray air showers is a potentially powerful new detection mechanism for studying spectrum and composition of ultra high energy cosmic rays that needs ...to be understood in greater detail. The radiation consists in large part of geosynchrotron radiation. The intensity of this radiation depends, among other factors, on the energy of the primary particle and the angle of the shower axis with respect to the geomagnetic field. Aims.Since the radiation mechanism is based on particle acceleration, the atmospheric electric field can play an important role. Especially inside thunderclouds large electric fields can be present. In this paper we examine the contribution of an electric field to the emission mechanism theoretically and experimentally. Methods.Two mechanisms of amplification of radio emission are considered: the acceleration radiation of the shower particles and the radiation from the current that is produced by ionization electrons moving in the electric field. For both mechanisms analytical estimates are made of their effects on the radio pulse height. We selected lopes data recorded during thunderstorms, periods of heavy cloudiness and periods of cloudless weather. We tested whether the correlations with geomagnetic angle and primary energy vary with atmospheric conditions. Results.We find that during thunderstorms the radio emission can be strongly enhanced. The present data suggests that the observed amplification is caused by acceleration of the shower electrons and positrons. In the near future, extensions of lopes and the construction of lofar will help to identify the mechanism in more detail. No amplified pulses were found during periods of cloudless sky or heavy cloudiness, suggesting that the electric field effect for radio air shower measurements can be safely ignored during non-thunderstorm conditions.
A comparison of the coincidence summing correction methods is presented. Since there are several ways for computing these corrections, each method has advantages and drawbacks that could be compared. ...This part of the comparison was restricted to point sources. The same experimental spectra, decay scheme and photon emission intensities were used by all the participants. The results were expressed as coincidence summing correction factors for several energies of
152Eu and
134Cs, and three source-to-detector distances. They are presented and discussed.
Radio emission from particle showers can be used as a method of neutrino detection in the high and very high energy range as a Cherenkov pulse originates from the charge excess developing in the ...medium. Our study presents simulations of neutrino induced showers in rock salt and the radio emission that they generate, using the HERWIG, GEANT4 and AIRES codes. We have performed a complete study of all neutrino flavours interacting on nuclei, both for charged-current and neutral-current interactions, using the knowledge and codes available today. As primary neutrino energies we have chosen three values: 1012eV, 1015eV and 1017eV. We have injected all the particles resulting from the first interactions into shower simulation codes.
Salt is one of the dielectric media proposed for radio detection of neutrinos already in the sixties of last century, and can be found in large volumes throughout the world.
The calculation of the radio signal was performed considering the entire shower evolution, by approximating the shower with a current density. We have taken into account, in the equations, only the longitudinal profile. The aim of this study is to investigate whether different interactions can be discriminated in an experiment for detection of high energy particles based on the radio emission from the showers they initiate in a dense medium. For this we have performed and systematically analyzed simulations from several points of view.
Aims. We wish to study the spectral dependence of the radio emission from cosmic-ray air showers around $100~{\rm PeV}$ $(10^{17}~{\rm eV})$. Methods. We observe short radio pulses in a broad ...frequency band with the dipole-interferometer LOPES (LOFAR Prototype Station), which is triggered by a particle detector array named Karlsruhe Shower Core and Array Detector (KASCADE). LOFAR is the Low Frequency Array. For this analysis, 23 strong air shower events are selected using parameters from KASCADE. The radio data are digitally beam-formed before the spectra are determined by sub-band filtering and fast Fourier transformation. Results. The resulting electric field spectra fall off to higher frequencies. An average electric field spectrum is fitted with an exponential $E_{\nu}=K\cdot\mbox{exp}\,(\nu/\mathrm{MHz}/\beta)$ and $\beta=-0.017\pm0.004$, or alternatively, with a power law $\epsilon_{\nu}=K\cdot\nu^{\alpha}$ and a spectral index of $\alpha=-1\pm0.2$. The spectral slope obtained is not consistent within uncertainties and it is slightly steeper than the slope obtained from Monte Carlo simulations based on air showers simulated with CORSIKA (Cosmic Ray Simulations for KASCADE). For the analyzed sample of LOPES events, we do not find any significant dependence of the spectral slope on the electric field amplitude, the azimuth angle, the zenith angle, the curvature radius, nor on the average distance of the antennae from the shower core position. But one of the strongest events was measured during thunderstorm activity in the vicinity of LOPES and shows the longest pulse length measured of $110~\mathrm{ns}$ and a spectral slope of $\alpha=-3.6$. Conclusions. We show with two different methods that frequency spectra from air shower radio emission can be reconstructed on event-by-event basis, with only two dozen dipole antennae simultaneously over a broad range of frequencies. According to the obtained spectral slopes, the maximum power is emitted below 40 MHz. Furthermore, the decrease in power to higher frequencies indicates a loss in coherence determined by the shower disc thickness. We conclude that a broader bandwidth, larger collecting area, and longer baselines, as will be provided by LOFAR, are necessary to further investigate the relation of the coherence, pulse length, and spectral slope of cosmic ray air showers.
The KASCADE and KASCADE-Grande experiments operated in KIT-Campus North, Karlsruhe (Germany) from 1993 to 2012. The two experiments studied primary cosmic rays in the energy range from 10
14
eV to 10
...18
eV, investigating the change of slope of the spectrum detected at 2 - 4 × 10
15
eV, the so called knee. We briefly review the performance of the experiments and then the main results obtained in the operation of both experiments: the test of hadronic interaction models, the all particle primary spectrum, the elemental composition of primary cosmic rays (with the first claim of a knee-like feature of the heavy primaries spectrum) and the search for large scale anisotropies.
Latest results from the KASCADE-Grande experiment Chiavassa, A.; Apel, W.D.; Arteaga-Velázquez, J.C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2014, Letnik:
742
Journal Article
Recenzirano
Odprti dostop
The KASCADE-Grande experiment operated at KIT from January 2004 to November 2012, measuring EAS generated by primary cosmic rays in the 1016–1018eV energy range. The experiment detected, for each ...single event, with a high resolution, the total number of charged particles (Nch) and of muons (Nμ).
In this contribution we present the latest results about:(i)The measurement of the all particle energy spectrum, discussing the influence of the hadronic interaction model used to derive the energy calibration of the experimental data.(ii)The energy spectra derived separating the events according to the Nμ/Nch ratio. This technique allowed us to unveil a steepening of the spectrum of heavy primaries at E~1016.92±0.04eV and a hardening of the spectrum of light primaries at E~1017.08±0.08eV.(iii)The elemental spectra (for five mass groups) obtained applying a detailed unfolding analysis technique.(iv)A search for large scale anisotropies.
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