1,382 research outputs found
Testing the proposed link between cosmic rays and cloud cover
A decrease in the globally averaged low level cloud cover, deduced from the
ISCCP infra red data, as the cosmic ray intensity decreased during the solar
cycle 22 was observed by two groups. The groups went on to hypothesise that the
decrease in ionization due to cosmic rays causes the decrease in cloud cover,
thereby explaining a large part of the presently observed global warming. We
have examined this hypothesis to look for evidence to corroborate it. None has
been found and so our conclusions are to doubt it. From the absence of
corroborative evidence, we estimate that less than 23%, at the 95% confidence
level, of the 11-year cycle change in the globally averaged cloud cover
observed in solar cycle 22 is due to the change in the rate of ionization from
the solar modulation of cosmic rays
Effects of CO\u3csub\u3e2\u3c/sub\u3e on Growth Rate, C:N:P, and Fatty Acid Composition of Seven Marine Phytoplankton Species
Carbon dioxide (CO2) is the primary substrate for photosynthesis by the phytoplankton that form the base of the marine food web and mediate biogeochemical cycling of C and nutrient elements. Specific growth rate and elemental composition (C:N:P) were characterized for 7 cosmopolitan coastal and oceanic phytoplankton species (5 diatoms and 2 chlorophytes) using low density, nutrient-replete, semi-continuous culture experiments in which CO2 was manipulated to 4 levels ranging from post-bloom/glacial maxima (ppm) to geological maxima levels (\u3e2900 ppm). Specific growth rates at high CO2 were from 19 to 60% higher than in low CO2 treatments in 4 species and 44% lower in 1 species; there was no significant change in 2 species. Higher CO2 availability also resulted in elevated C:P and N:P molar ratios in Thalassiosira pseudonana (~60 to 90% higher), lower C:P and N:P molar ratios in 3 species (~20 to 50% lower), and no change in 3 species. Carbonate system-driven changes in growth rate did not necessarily result in changes in elemental composition, or vice versa. In a subset of 4 species for which fatty acid composition was examined, elevated CO2 did not affect the contribution of polyunsaturated fatty acids to total fatty acids significantly. These species show relatively little sensitivity between present day CO2 and predicted ocean acidification scenarios (year 2100). The results, however, demonstrate that CO2 availability at environmentally and geologically relevant scales can result in large changes in phytoplankton physiology, with potentially large feedbacks to ocean biogeochemical cycles and ecosystem structure
Measurements of Smoke Characteristics in HVAC Ducts
Research paper published in the journal Fire Technology in 2001The characteristics of smoke traveling in an HVAC duct have been observed along with the response of selected duct smoke detectors. The simulated HVAC system consists of a 9 m long duct, 0.45 m in diameter. An exhaust fan is placed at one end of the duct and is capable of inducing airflow rates that range from 0 to 1.5 m
3
/s. The flow is controlled by means of a manual damper. On the upstream end of the duct there is a square exhaust hood approximately 2.2 m at the bottom and 0.3 m at the top. The bottom of the hood is approximately 2.5 m above the floor a shroud extends down to approximately 1.5 m above the floor. The test section, placed immediately downstream of the hood, is 3.5 m long duct with a square cross section of 0.4 m on a side. The instrumentation includes oxygen, carbon monoxide and carbon dioxide gas analyzers and a load cell to determine the energy release rate of the fires tested. The smoke within the duct is characterized by means of a laser light sheet and CCD camera, two white light source and photocell ensembles, a Pitot tube and an array of eight thermocouples placed on the vertical plane of symmetry. A smoke detector was placed at the downstream end of the test section. Two types of detectors were tested, ionization and photoelectric, with a single sampling probe geometry. The fires tested cover a wide range of fuels (propane, heptane, toluene, toluene/heptane mixture, shredded paper, polyurethane foam, wood cribs) with the peak energy release rates up to 800 kW. The smoke detector performance, temperature, flow field, smoke particle size and particle distributions are dependent on the fire characteristics and airflow through the duct. The different measurements could be scaled by means of the fire size and airflow rate but left a strong dependency on the fuel and burning characteristics (i.e. smoldering, flaming). The optical density and mass optical density are analyzed as metrics for characterizing smoke and smoke detector response. Detailed comparisons between the different metrics used are presented throughout this work. Clear evidence of stratification and aging of the smoke along the duct are also presented. The limitations of the present configuration and the need for a larger scale study are also discussed
Results from the KASCADE, KASCADE-Grande, and LOPES experiments
The origin of high-energy cosmic rays in the energy range from 10^14 to 10^18
eV is explored with the KASCADE and KASCADE-Grande experiments. Radio signals
from air showers are measured with the LOPES experiment. An overview on results
is given.Comment: Talk at The ninth International Conference on Topics in Astroparticle
and Underground Physics, TAUP 2005, Zaragoza, September 10-14, 200
Performance of fully instrumented detector planes of the forward calorimeter of a Linear Collider detector
Detector-plane prototypes of the very forward calorimetry of a future
detector at an e+e- collider have been built and their performance was measured
in an electron beam. The detector plane comprises silicon or GaAs pad sensors,
dedicated front-end and ADC ASICs, and an FPGA for data concentration.
Measurements of the signal-to-noise ratio and the response as a function of the
position of the sensor are presented. A deconvolution method is successfully
applied, and a comparison of the measured shower shape as a function of the
absorber depth with a Monte-Carlo simulation is given.Comment: 25 pages, 32 figures, revised version following comments from
referee
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
Radio emission of highly inclined cosmic ray air showers measured with LOPES
LOPES-10 (the first phase of LOPES, consisting of 10 antennas) detected a
significant number of cosmic ray air showers with a zenith angle larger than
50, and many of these have very high radio field strengths. The most
inclined event that has been detected with LOPES-10 has a zenith angle of
almost 80. This is proof that the new technique is also applicable
for cosmic ray air showers with high inclinations, which in the case that they
are initiated close to the ground, can be a signature of neutrino events.Our
results indicate that arrays of simple radio antennas can be used for the
detection of highly inclined air showers, which might be triggered by
neutrinos. In addition, we found that the radio pulse height (normalized with
the muon number) for highly inclined events increases with the geomagnetic
angle, which confirms the geomagnetic origin of radio emission in cosmic ray
air showers.Comment: A&A accepte
Radio emission of highly inclined cosmic ray air showers measured with LOPES
LOPES (LOFAR Prototype Station) is an array of dipole antennas used for
detection of radio emission from air showers. It is co-located and triggered by
the KASCADE (Karlsruhe Shower Core and Array Detector) experiment, which also
provides informations about air shower properties. Even though neither LOPES
nor KASCADE are completely optimized for the detection of highly inclined
events, a significant number of showers with zenith angle larger than 50
have been detected in the radio domain, and many with very high field
strengths. Investigation of inclined showers can give deeper insight into the
nature of primary particles that initiate showers and also into the possibility
that some of detected showers are triggered by neutrinos. In this paper, we
show the example of such an event and present some of the characteristics of
highly inclined showers detected by LOPES
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