5,635 research outputs found
The Electrostatic Ion Beam Trap : a mass spectrometer of infinite mass range
We study the ions dynamics inside an Electrostatic Ion Beam Trap (EIBT) and
show that the stability of the trapping is ruled by a Hill's equation. This
unexpectedly demonstrates that an EIBT, in the reference frame of the ions
works very similar to a quadrupole trap. The parallelism between these two
kinds of traps is illustrated by comparing experimental and theoretical
stability diagrams of the EIBT. The main difference with quadrupole traps is
that the stability depends only on the ratio of the acceleration and trapping
electrostatic potentials, not on the mass nor the charge of the ions. All kinds
of ions can be trapped simultaneously and since parametric resonances are
proportional to the square root of the charge/mass ratio the EIBT can be used
as a mass spectrometer of infinite mass range
Shape in an Atom of Space: Exploring quantum geometry phenomenology
A phenomenology for the deep spatial geometry of loop quantum gravity is
introduced. In the context of a simple model, an atom of space, it is shown how
purely combinatorial structures can affect observations. The angle operator is
used to develop a model of angular corrections to local, continuum flat-space
3-geometries. The physical effects involve neither breaking of local Lorentz
invariance nor Planck scale suppression, but rather reply on only the
combinatorics of SU(2) recoupling. Bhabha scattering is discussed as an example
of how the effects might be observationally accessible.Comment: 14 pages, 7 figures; v2 references adde
Neutralizing antibody response during acute and chronic hepatitis C virus infection
Little is known about the role of Abs in determining the outcome of hepatitis C virus (HCV) infection. By using infectious retroviral pseudotypes bearing HCV glycoproteins, we measured neutralizing Ab (nAb) responses during acute and chronic HCV infection. In seven acutely infected health care workers, only two developed a nAb response that failed to associate with viral clearance. In contrast, the majority of chronically infected patients had nAbs. To determine the kinetics of strain-specific and crossreactive nAb emergence, we studied patient H, the source of the prototype genotype 1a H77 HCV strain. An early weak nAb response, specific for the autologous virus, was detected at seroconversion. However, neutralization of heterologous viruses was detected only between 33 and 111 weeks of infection. We also examined the development of nAbs in 10 chimpanzees infected with H77 clonal virus. No nAb responses were detected in three animals that cleared virus, whereas strain-specific nAbs were detected in six of the seven chronically infected animals after approximately 50 weeks of infection. The delayed appearance of high titer crossreactive nAbs in chronically infected patients suggests that selective mechanism(s) may operate to prevent the appearance of these Abs during acute infection. The long-term persistence of these nAbs in chronically infected patients may regulate viral replication
About the dynamics and thermodynamics of trapped ions
This tutorial introduces the dynamics of charged particles in a
radiofrequency trap in a very general manner to point out the differences
between the dynamics in a quadrupole and in a multipole trap. When dense
samples are trapped, the dynamics is modified by the Coulomb repulsion between
ions. To take into account this repulsion, we propose to use a method,
originally developed for particles in Penning trap, that model the ion cloud as
a cold fluid. This method can not reproduce the organisation of cold clouds as
crystals but it allows one to scale the size of large samples with the trapping
parameters and the number of ions trapped, for different linear geometries of
trap.Comment: accepted for publication in the "Modern Applications of Trapped Ions"
special issu
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University Lands Advanced Recovery Initative
Hydrocarbon production from West Texas lands held by The University of Texas System has been in decline since the 1960s (fig. 1). Nonetheless, analysis of resources on University lands indicates that of the 7,252 million stock tank barrels (MMSTB) of original oil in place, only 1,679 MMSTB has been recovered since production was established early in this century, and only 150 MMSTB of reserves exist. Unless advanced development practices are applied to University lands fields, some 5,423 MMSTB will therefore remain unrecovered in existing fields. Importantly, 2,140 MMSTB of this resource, nearly one-third of the original oil in place, is mobile oil that can be recovered using standard drilling and completion practices, provided that wellbores and completion intervals are geologically targeted to access this unrecovered resource (fig. 2).
The goal of the University Lands Advanced Recovery Initiative is to characterize selected University Lands reservoirs to aid operators in geologically targeting the remaining hydrocarbon resource to stem the decline in University Lands production. This project is funded by The University of Texas (U.T.) System and by matching funds from operators of University Lands fields chosen for site-specific studies. The agreement between the Bureau of Economic Geology and the U.T. System was finalized on July 29, 1996. Three individual site-specific projects have been initiated in the first year of the project: (1) Fuhrman-Mascho Block 10 Unit, a San Andres-Grayburg carbonate and sandstone reservoir in Andrews County operated by Arrow Operating Company, (2) University Waddell Devonian field, a Devonian chert reservoir in Crane County operated by Pennzoil, and (3) North McElroy Grayburg field, a Grayburg carbonate reservoir in Crane and Upton Counties newly acquired by Apache Corporation (fig. 3). Fuhrman-Mascho and University Waddell fields have recovery efficiencies significantly below that of comparable fields within the same geologically based play. McElroy field, although producing at an efficiency above play average, contains an enormous 832 million barrels of unrecovered mobile oil (table 1).Bureau of Economic Geolog
Holographic Formulation of Quantum Supergravity
We show that supergravity with a cosmological constant can be
expressed as constrained topological field theory based on the supergroup
. The theory is then extended to include timelike boundaries with
finite spatial area. Consistent boundary conditions are found which induce a
boundary theory based on a supersymmetric Chern-Simons theory. The boundary
state space is constructed from states of the boundary supersymmetric
Chern-Simons theory on the punctured two sphere and naturally satisfies the
Bekenstein bound, where area is measured by the area operator of quantum
supergravity.Comment: 30 pages, no figur
Penning traps as a versatile tool for precise experiments in fundamental physics
This review article describes the trapping of charged particles. The main
principles of electromagnetic confinement of various species from elementary
particles to heavy atoms are briefly described. The preparation and
manipulation with trapped single particles, as well as methods of frequency
measurements, providing unprecedented precision, are discussed. Unique
applications of Penning traps in fundamental physics are presented.
Ultra-precise trap-measurements of masses and magnetic moments of elementary
particles (electrons, positrons, protons and antiprotons) confirm
CPT-conservation, and allow accurate determination of the fine-structure
constant alpha and other fundamental constants. This together with the
information on the unitarity of the quark-mixing matrix, derived from the
trap-measurements of atomic masses, serves for assessment of the Standard Model
of the physics world. Direct mass measurements of nuclides targeted to some
advanced problems of astrophysics and nuclear physics are also presented
Spatial Hypersurfaces in Causal Set Cosmology
Within the causal set approach to quantum gravity, a discrete analog of a
spacelike region is a set of unrelated elements, or an antichain. In the
continuum approximation of the theory, a moment-of-time hypersurface is well
represented by an inextendible antichain. We construct a richer structure
corresponding to a thickening of this antichain containing non-trivial
geometric and topological information. We find that covariant observables can
be associated with such thickened antichains and transitions between them, in
classical stochastic growth models of causal sets. This construction highlights
the difference between the covariant measure on causal set cosmology and the
standard sum-over-histories approach: the measure is assigned to completed
histories rather than to histories on a restricted spacetime region. The
resulting re-phrasing of the sum-over-histories may be fruitful in other
approaches to quantum gravity.Comment: Revtex, 12 pages, 2 figure
Dynamics of axialized laser-cooled ions in a Penning trap
We report the experimental characterization of axialization - a method of
reducing the magnetron motion of a small number of ions stored in a Penning
trap. This is an important step in the investigation of the suitability of
Penning traps for quantum information processing. The magnetron motion was
coupled to the laser-cooled modified cyclotron motion by the application of a
near-resonant oscillating quadrupole potential (the "axialization drive").
Measurement of cooling rates of the radial motions of the ions showed an
order-of-magnitude increase in the damping rate of the magnetron motion with
the axialization drive applied. The experimental results are in good
qualitative agreement with a recent theoretical study. In particular, a
classical avoided crossing was observed in the motional frequencies as the
axialization drive frequency was swept through the optimum value, proving that
axialization is indeed a resonant effect.Comment: 8 pages, 9 figure
Conceptual design study for heat exhaust management in the ARC fusion pilot plant
The ARC pilot plant conceptual design study has been extended beyond its
initial scope [B. N. Sorbom et al., FED 100 (2015) 378] to explore options for
managing ~525 MW of fusion power generated in a compact, high field (B_0 = 9.2
T) tokamak that is approximately the size of JET (R_0 = 3.3 m). Taking
advantage of ARC's novel design - demountable high temperature superconductor
toroidal field (TF) magnets, poloidal magnetic field coils located inside the
TF, and vacuum vessel (VV) immersed in molten salt FLiBe blanket - this
follow-on study has identified innovative and potentially robust power exhaust
management solutions.Comment: Accepted by Fusion Engineering and Desig
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