1,494 research outputs found
Gause's exclusion principle revisited: artificial modified species and competition
Gause's principle of competition between two species is studied when one of
them is sterile. We study the condition for total extinction in the niche,
namely, when the sterile population exterminates the native one by an optimal
use of resources. A mathematical Lotka-Volterra non linear model of interaction
between a native and sterile species is proposed. The condition for total
extinction is related to the initial number of sterile individuals
released in the niche. In fact, the existence of a critical sterile-population
value is conjectured from numerical analysis and an analytical
estimation is found. When spatial diffusion (migration) is considered a
critical size territory is found and, for small territory, total extinction
exist in any case. This work is motived by the extermination agriculture
problem of fruit flies in our region.Comment: 11 pages. Published in Jour.Phys.A Math.Gen. 33, 4877 (2000
ALBA HIGH VOLTAGE SPLITTER -POWER DISTRIBUTION TO ION PUMPS
Abstract High Voltage Splitter (HVS) is an equipment designed in Alba that allows a high voltage (HV) distribution (up to +7kV) from one ion pump controller up to eight ion pumps. Using it, the total number of high voltage power supplies needed in Alba's vacuum installation has decreased significantly. The current drawn by each splitter channel is measured independently inside a range from 10nA up to 10mA with 5% accuracy, those measurements are a base for vacuum pressure calculations. A relation, current-pressure depends mostly on the ion pump type, so different tools providing the full calibration flexibility have been implemented. Splitter settings, status and recorded data are accessible over a 10/100 Base-T Ethernet network, none the less a local (manual) control was implemented mostly for service purposes. The device supports also additional functions as a HV cable interlock, pressure interlock output cooperating with the facility's Equipment Protection System (EPS, ref: [1]), programmable pressure warnings/alarms and automatic calibration process based on an external current source. This paper describes the project, functionality, implementation, installation and operation as a part of the vacuum system at Alba
The Origin of the Universe as Revealed Through the Polarization of the Cosmic Microwave Background
Modern cosmology has sharpened questions posed for millennia about the origin
of our cosmic habitat. The age-old questions have been transformed into two
pressing issues primed for attack in the coming decade: How did the Universe
begin? and What physical laws govern the Universe at the highest energies? The
clearest window onto these questions is the pattern of polarization in the
Cosmic Microwave Background (CMB), which is uniquely sensitive to primordial
gravity waves. A detection of the special pattern produced by gravity waves
would be not only an unprecedented discovery, but also a direct probe of
physics at the earliest observable instants of our Universe. Experiments which
map CMB polarization over the coming decade will lead us on our first steps
towards answering these age-old questions.Comment: Science White Paper submitted to the US Astro2010 Decadal Survey.
Full list of 212 author available at http://cmbpol.uchicago.ed
A Monte Carlo simulation of the Sudbury Neutrino Observatory proportional counters
The third phase of the Sudbury Neutrino Observatory (SNO) experiment added an
array of 3He proportional counters to the detector. The purpose of this Neutral
Current Detection (NCD) array was to observe neutrons resulting from
neutral-current solar neutrino-deuteron interactions. We have developed a
detailed simulation of the current pulses from the NCD array proportional
counters, from the primary neutron capture on 3He through the NCD array
signal-processing electronics. This NCD array Monte Carlo simulation was used
to model the alpha-decay background in SNO's third-phase 8B solar-neutrino
measurement.Comment: 38 pages; submitted to the New Journal of Physic
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Searches For High-Frequency Variations In The B-8 Solar Neutrino Flux At The Sudbury Neutrino Observatory
We have performed three searches for high-frequency signals in the solar neutrino flux measured by the Sudbury Neutrino Observatory, motivated by the possibility that solar g-mode oscillations could affect the production or propagation of solar B-8 neutrinos. The first search looked for any significant peak in the frequency range 1-144 day(-1), with a sensitivity to sinusoidal signals with amplitudes of 12% or greater. The second search focused on regions in which g-mode signals have been claimed by experiments aboard the Solar and Heliospheric Observatory satellite, and was sensitive to signals with amplitudes of 10% or greater. The third search looked for extra power across the entire frequency band. No statistically significant signal was detected in any of the three searches.Natural Sciences and Engineering Research Council, CanadaIndustry Canada, CanadaNational Research Council, CanadaNorthern Ontario Heritage Fund, CanadaAtomic Energy of Canada, Ltd., CanadaOntario Power Generation, CanadaHigh Performance Computing Virtual Laboratory, CanadaCanada Foundation for InnovationDept. of Energy, USNational Energy Research Scientific Computing Center, USScience and Technologies Facilities Council, UKAstronom
Microwave amplification with nanomechanical resonators
Sensitive measurement of electrical signals is at the heart of modern science
and technology. According to quantum mechanics, any detector or amplifier is
required to add a certain amount of noise to the signal, equaling at best the
energy of quantum fluctuations. The quantum limit of added noise has nearly
been reached with superconducting devices which take advantage of
nonlinearities in Josephson junctions. Here, we introduce a new paradigm of
amplification of microwave signals with the help of a mechanical oscillator. By
relying on the radiation pressure force on a nanomechanical resonator, we
provide an experimental demonstration and an analytical description of how the
injection of microwaves induces coherent stimulated emission and signal
amplification. This scheme, based on two linear oscillators, has the advantage
of being conceptually and practically simpler than the Josephson junction
devices, and, at the same time, has a high potential to reach quantum limited
operation. With a measured signal amplification of 25 decibels and the addition
of 20 quanta of noise, we anticipate near quantum-limited mechanical microwave
amplification is feasible in various applications involving integrated
electrical circuits.Comment: Main text + supplementary information. 14 pages, 3 figures (main
text), 18 pages, 6 figures (supplementary information
Nanomechanical motion measured with precision beyond the standard quantum limit
Nanomechanical oscillators are at the heart of ultrasensitive detectors of
force, mass and motion. As these detectors progress to even better sensitivity,
they will encounter measurement limits imposed by the laws of quantum
mechanics. For example, if the imprecision of a measurement of an oscillator's
position is pushed below the standard quantum limit (SQL), quantum mechanics
demands that the motion of the oscillator be perturbed by an amount larger than
the SQL. Minimizing this quantum backaction noise and nonfundamental, or
technical, noise requires an information efficient measurement. Here we
integrate a microwave cavity optomechanical system and a nearly noiseless
amplifier into an interferometer to achieve an imprecision below the SQL. As
the microwave interferometer is naturally operated at cryogenic temperatures,
the thermal motion of the oscillator is minimized, yielding an excellent force
detector with a sensitivity of 0.51 aN/rt(Hz). In addition, the demonstrated
efficient measurement is a critical step towards entangling mechanical
oscillators with other quantum systems.Comment: 5 pages, 4 figure
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