605 research outputs found
An antisense RNA expression vector for Neurospora crassa
The artificial expression of antisense RNA is commonly used in eucaryotes, especially higher plants, to reduce the level of specific proteins (van der Krol et al. 1988 Nature 333:866-869). Here we report the use of antisense RNA to inhibit the translation of a subunit of the mitochondrial NADH:ubiquinone oxidoreductase, the respiratory complex I in N. crass
New method for the time calibration of an interferometric radio antenna array
Digital radio antenna arrays, like LOPES (LOFAR PrototypE Station), detect
high-energy cosmic rays via the radio emission from atmospheric extensive air
showers. LOPES is an array of dipole antennas placed within and triggered by
the KASCADE-Grande experiment on site of the Karlsruhe Institute of Technology,
Germany. The antennas are digitally combined to build a radio interferometer by
forming a beam into the air shower arrival direction which allows measurements
even at low signal-to-noise ratios in individual antennas. This technique
requires a precise time calibration. A combination of several calibration steps
is used to achieve the necessary timing accuracy of about 1 ns. The group
delays of the setup are measured, the frequency dependence of these delays
(dispersion) is corrected in the subsequent data analysis, and variations of
the delays with time are monitored. We use a transmitting reference antenna, a
beacon, which continuously emits sine waves at known frequencies. Variations of
the relative delays between the antennas can be detected and corrected for at
each recorded event by measuring the phases at the beacon frequencies.Comment: 9 pages, 9 figures, 1 table, pre-print of article published in
Nuclear Inst. and Methods in Physics Research, A, available at:
http://www.sciencedirect.com/science/article/B6TJM-4Y9CF4B-4/2/37bfcb899a0f387d9875a5a0729593a
Absolute calibration of the LOPES antenna system
Radio emission in extensive air showers arises from an interaction with the
geomagnetic field and is subject of theoretical studies. This radio emission
has advantages for the detection of high energy cosmic rays compared to
secondary particle or fluorescence measurement methods. Radio antennas like the
LOPES30 antenna system are suited to investigate this emission process by
detecting the radio pulses. The characteristic observable parameters like
electric field strength and pulse length require a calibration which was done
with a reference radio source resulting in an amplification factor representing
the system behavior in the environment of the KASCADE-Grande experiment.
Knowing the amplification factor and the gain of the LOPES antennas LOPES30 is
calibrated absolutely for systematic analyses of the radio emission.Comment: 5 pages, Proceedings of International Workshop on Acoustic and Radio
EeV Neutrino detection Activities: ARENA, May 17-19, 2005, DESY Zeuthe
Space Environmental Effects Testing Capability at the Marshall Space Flight Center
Understanding the effects of the space environment on materials and systems is fundamental and essential for mission success. If not properly understood and designed for, the effects of the environment can lead to degradation of materials, reduction of functional lifetime, and system failure. In response to this need, the Marshall Space Flight Center has developed world class Space Environmental Effects (SEE) expertise and test facilities to simulate the space environment. Capabilities include multiple unique test systems comprising the most complete SEE testing capability available. These test capabilities include charged particle radiation (electrons, protons, ions), ultraviolet radiation (UV), vacuum ultraviolet radiation (VUV), atomic oxygen, plasma effects, space craft charging, lunar surface and planetary effects, vacuum effects, and hypervelocity impacts as well as the combination of these capabilities. In addition to the uniqueness of the individual test capabilities, MSFC is the only NASA facility where the effects of the different space environments can be tested in one location. Combined with additional analytical capabilities for pre- and post-test evaluation, MSFC is a one-stop shop for materials testing and analysis. The SEE testing and analysis are performed by a team of award winning experts nationally recognized for their contributions in the study of the effects of the space environment on materials and systems. With this broad expertise in space environmental effects and the variety of test systems and equipment available, MSFC is able to customize tests with a demonstrated ability to rapidly adapt and reconfigure systems to meet customers needs. Extensive flight experiment experience bolsters this simulation and analysis capability with a comprehensive understanding of space environmental effects
Spectral and Photophysical Studies of Poly[2,6-(1,5-dioctylnaphthalene)]thiophenes
A complete spectroscopic and photophysical study of three alternating naphthalene-α-thiophene copolymers was undertaken in solution (room and low temperature) and in the solid state (thin films in a Zeonex matrix). The study comprises absorption, emission, and tripletâtriplet spectra together with quantitative measurements of quantum yield (fluorescence, intersystem-crossing, internal conversion, and singlet oxygen formation) lifetimes and singlet and triplet energies. The overall data allow the determination of the rate constants for all the decay processes. Comparison between the behavior of analogous 1-naphthyl(oligo)thiophenes and the 2,6-naphthalene(oligo)thiophene copolymers allows several important observations. First, the polymers display higher fluorescence quantum yields and lower S1âT1 intersystem-crossing yields than the oligomers. This can be attributed to the presence of the 1,5-dioctyloxynaphthalene groups in the copolymers leading to a more rigid polymer backbone, which decreases radiationless deactivation and increases the radiative efficiency. Second, the singlet and triplet energies are significantly lower in the polymers than with the corresponding oligomers. This implies a lower HOMOâLUMO energy difference in the polymers due to an extended Ï-delocalization. Third, the singlet-to-triplet (S1âT1) energy splitting is higher in the oligomers than with the polymers, even though the former display higher intersystem-crossing yields. It is suggested that this may result from intersystem-crossing in the oligomers involving significant charge-transfer (CT) character (spin-orbit coupling is mediated by CT mixing involving the singlet and triplet states in matrix elements of the type 1ΚCT |Hâ|3Κ1) of the relevant excited states but that is less important with the polymers. We believe that this may be relevant to understanding the nature of CT states in conjugated copolymers
On noise treatment in radio measurements of cosmic ray air showers
Precise measurements of the radio emission by cosmic ray air showers require
an adequate treatment of noise. Unlike to usual experiments in particle
physics, where noise always adds to the signal, radio noise can in principle
decrease or increase the signal if it interferes by chance destructively or
constructively. Consequently, noise cannot simply be subtracted from the
signal, and its influence on amplitude and time measurement of radio pulses
must be studied with care. First, noise has to be determined consistently with
the definition of the radio signal which typically is the maximum field
strength of the radio pulse. Second, the average impact of noise on radio pulse
measurements at individual antennas is studied for LOPES. It is shown that a
correct treatment of noise is especially important at low signal-to-noise
ratios: noise can be the dominant source of uncertainty for pulse height and
time measurements, and it can systematically flatten the slope of lateral
distributions. The presented method can also be transfered to other experiments
in radio and acoustic detection of cosmic rays and neutrinos.Comment: 4 pages, 6 figures, submitted to NIM A, Proceedings of ARENA 2010,
Nantes, Franc
The LOPES experiment - recent results, status and perspectives
The LOPES experiment at the Karlsruhe Institute of Technology has been taking
radio data in the frequency range from 40 to 80 MHz in coincidence with the
KASCADE-Grande air shower detector since 2003. Various experimental
configurations have been employed to study aspects such as the energy scaling,
geomagnetic dependence, lateral distribution, and polarization of the radio
emission from cosmic rays. The high quality per-event air shower information
provided by KASCADE-Grande has been the key to many of these studies and has
even allowed us to perform detailed per-event comparisons with simulations of
the radio emission. In this article, we give an overview of results obtained by
LOPES, and present the status and perspectives of the ever-evolving experiment.Comment: Proceedings of the ARENA2010 conference, Nantes, Franc
Radio Emission in Atmospheric Air Showers: First Measurements with LOPES-30
When Ultra High Energy Cosmic Rays interact with particles in the Earth's
atmosphere, they produce a shower of secondary particles propagating toward the
ground. LOPES-30 is an absolutely calibrated array of 30 dipole antennas
investigating the radio emission from these showers in detail and clarifying if
the technique is useful for largescale applications. LOPES-30 is co-located and
measures in coincidence with the air shower experiment KASCADE-Grande. Status
of LOPES-30 and first measurements are presented.Comment: Proceedings of ARENA 06, June 2006, University of Northumbria, U
Amplitude calibration of a digital radio antenna array for measuring cosmic ray air showers
Radio pulses are emitted during the development of air showers, where air
showers are generated by ultra-high energy cosmic rays entering the Earth's
atmosphere. These nanosecond short pulses are presently investigated by various
experiments for the purpose of using them as a new detection technique for
cosmic particles. For an array of 30 digital radio antennas (LOPES experiment)
an absolute amplitude calibration of the radio antennas including the full
electronic chain of the data acquisition system is performed, in order to
estimate absolute values of the electric field strength for these short radio
pulses. This is mandatory, because the measured radio signals in the MHz
frequency range have to be compared with theoretical estimates and with
predictions from Monte Carlo simulations to reconstruct features of the primary
cosmic particle. A commercial reference radio emitter is used to estimate
frequency dependent correction factors for each single antenna of the radio
antenna array. The expected received power is related to the power recorded by
the full electronic chain. Systematic uncertainties due to different
environmental conditions and the described calibration procedure are of order
20%.Comment: Article accepted by Nuclear Instruments and Methods in Physics
Research, A (NIM A
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