3,779 research outputs found
How can a 22-pole ion trap exhibit 10 local minima in the effective potential?
The column density distribution of trapped OH ions in a 22-pole ion trap
is measured for different trap parameters. The density is obtained from
position-dependent photodetachment rate measurements. Overall, agreement is
found with the effective potential of an ideal 22-pole. However, in addition we
observe 10 distinct minima in the trapping potential, which indicate a breaking
of the 22-fold symmetry. Numerical simulations show that a displacement of a
subset of the radiofrequency electrodes can serve as an explanation for this
symmetry breaking
Differential Scattering Cross-Sections for the Different Product Vibrational States in the Ion-Molecule Reaction Ar+ + N2
The charge transfer reaction Ar+ + N2 --> Ar + N2+ has been investigated in a
crossed beam experiment in combination with three-dimensional velocity map
imaging. Angular differential state-to-state cross sections were determined as
a function of the collision energy. We found that scattering into the first
excited vibrational level dominates as expected, but only for scattering in the
forward direction. Higher vibrational excitations up to v'=6 have been observed
for larger scattering angles. For decreasing collision energy, scattering into
higher scattering angles becomes increasingly important for all kinematically
allowed quantum states. Our detailed measurements indicate that a quantitative
agreement between experiment and theory for this basic ion-molecule reaction
now comes within reach.Comment: accepted to Phys. Rev. Let
Assessment of the development of aquifer management councils (COTAS) for sustainable groundwater management in Guanajuato, Mexico
Collective groundwater management by water usersâself-regulationâis increasingly advocated as a complement to state regulation. This article analyzes the attempts by the Guanajuato State Water Commission (CEAG) in central Mexico to promote user self-regulation through the establishment and development of 14 Consejos TĂ©cnicos de Aguas (COTAS; Technical Water Councils). Based on a joint assessment by a former senior CEAG policy-maker and two researchers, Guanajuatoâs groundwater-management policy is reviewed to understand why user self-regulation was less successful than expected. It concludes that increasing awareness and improving the knowledge base on groundwater is not enough to trigger self-regulation by groundwater users. A wider delegation of responsibilities to the COTAS is necessary, combined with: (1) functioning mechanisms for enforcing groundwater legislation, especially concerning well permits and pumped volumes, and (2) mechanisms that ensure the legitimacy and accountability of usersâ representatives to both users and state agencie
Focal plane transport assembly for the HEAO-B X-ray telescope
The High Energy Astronomy Observatory - Mission B (HEAO-B), an earth orbiting X-ray telescope facility capable of locating and imaging celestial X-ray sources within one second of arc in the celestial sphere, is considered. The Focal Plane Transport Assembly (FPTA) is one of the basic structural elements of the three thousand pound HEAO-B experiment payload. The FPTA is a multifunctional assembly which supports seven imaging X-ray detectors circumferentially about a central shaft and accurately positions any particular one into the focus of a high resolution mirror assembly. A drive system, position sensor, rotary coupler, and detent alignment system, all an integral part of the rotatable portion which in turn is supported by main bearings to the stationary focal plane housing are described
Photodetachment of cold OH- in a multipole ion trap
The absolute photodetachment cross section of OH- anions at a rotational and
translational temperature of 170K is determined by measuring the
detachment-induced decay rate of the anions in a multipole radio-frequency ion
trap. In comparison with previous results, the obtained cross section shows the
importance of the initial rotational state distribution. Using a tomography
scan of the photodetachment laser through the trapped ion cloud, the derived
cross section is model-independent and thus features a small systematic
uncertainty. The tomography also yields the column density of the OH- anions in
the 22-pole ion trap in good agreement with the expected trapping potential of
a large field free region bound by steep potential walls.Comment: Phys. Rev. Lett., in pres
Low-Frequency Characterization of Switched dc-dc Converters
Averaging techniques are developed here to represent buck, boost, and buck-boost types of switched dc-dc converters by approximate continuous models. Simple analytical expressions in terms of the circuit components are derived for the characteristic transient and frequency responses of timeaveraged (continuous) power-stage models for use in designing and understanding the behavior of corresponding switched power stages. Novel conclusions include the dependence of effective circuit component values upon switch duty ratio and the existence of a real positive zero in certain transfer functions. Responses from analog computer simulations of the switched and averaged power stages agree well and, in turn, confirm the analytic predictions. High-order systems can be analyzed by the averaging technique without a commensurate increase in complexity
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