1,343 research outputs found
Tracing Nitrogen in Volcanic and Geothermal Volatiles from the Nicaraguan Volcanic Front
We report new chemical and isotopic data from 26 volcanic and geothermal gases, vapor condensates, and thermal water samples,
collected along the Nicaraguan volcanic front. The samples were analyzed for chemical abundances and stable isotope compositions,
with a focus on nitrogen abundances and isotope ratios. These data are used to evaluate samples for volatile contributions from magma,
air, air-saturated water, and the crust. Samples devoid of crustal contamination (based upon He isotope composition) but slightly contaminated
by air or air-saturated water are corrected using N2/Ar ratios in order to obtain primary magmatic values, composed of contributions
from upper mantle and subducted hemipelagic sediment on the down-going plate. Using a mantle endmember with
d15N= 5&and N2/He = 100 and a subducted sediment component with d15N=+7& and N2/He = 10,500, the average sediment contribution
to Nicaraguan volcanic and geothermal gases was determined to be 71%. Most of the gases were dominated by sediment-derived
nitrogen, but gas from Volca´n Mombacho, the southernmost sampling location, had a mantle signature (46% from subducted
sediment, or 54% from the mantle) and an affinity with mantle-dominated gases discharging from Costa Rica localities to the south. High
CO2/N2 exc. ratios (N2 exc. is the N2 abundance corrected for contributions from air) in the south are similar to those in Costa Rica, and
reflect the predominant mantle wedge input, whereas low ratios in the north indicate contribution by altered oceanic crust and/or preferential
release of nitrogen over carbon from the subducting slab. Sediment-derived nitrogen fluxes at the Nicaraguan volcanic front,
estimated by three methods, are 7.8 · 108 mol N/a from 3He flux, 6.9 · 108 mol/a from SO2 flux, and 2.1 · 108 and 1.3 · 109 mol/a from
CO2 fluxes calculated from 3He and SO2, respectively. These flux results are higher than previous estimates for Central America, reflecting
the high sediment-derived volatile contribution and the high nitrogen content of geothermal and volcanic gases in Nicaragua. The
fluxes are also similar to but higher than estimated hemipelagic nitrogen inputs at the trench, suggesting addition of N from altered oceanic
basement is needed to satisfy these flux estimates. The similarity of the calculated input of N via the trench to our calculated outputs
suggests that little or none of the subducted nitrogen is being recycled into the deeper mantle, and that it is, instead, returned to the
surface via arc volcanism
Fractal Theory Space: Spacetime of Noninteger Dimensionality
We construct matter field theories in ``theory space'' that are fractal, and
invariant under geometrical renormalization group (RG) transformations. We
treat in detail complex scalars, and discuss issues related to fermions,
chirality, and Yang-Mills gauge fields. In the continuum limit these models
describe physics in a noninteger spatial dimension which appears above a RG
invariant ``compactification scale,'' M. The energy distribution of KK modes
above M is controlled by an exponent in a scaling relation of the vacuum energy
(Coleman-Weinberg potential), and corresponds to the dimensionality. For
truncated-s-simplex lattices with coordination number s the spacetime
dimensionality is 1+(3+2ln(s)/ln(s+2)). The computations in theory space
involve subtleties, owing to the 1+3 kinetic terms, yet the resulting
dimensionalites are equivalent to thermal spin systems. Physical implications
are discussed.Comment: 28 pages, 6 figures; Paper has been amplified with a more detailed
discussion of a number of technical issue
Langevin Simulations of Two Dimensional Vortex Fluctuations: Anomalous Dynamics and a New -exponent
The dynamics of two dimensional (2D) vortex fluctuations are investigated
through simulations of the 2D Coulomb gas model in which vortices are
represented by soft disks with logarithmic interactions. The simulations
trongly support a recent suggestion that 2D vortex fluctuations obey an
intrinsic anomalous dynamics manifested in a long range 1/t-tail in the vortex
correlations. A new non-linear IV-exponent a, which is different from the
commonly used AHNS exponent, a_AHNS and is given by a = 2a_AHNS - 3, is
confirmed by the simulations. The results are discussed in the context of
earlier simulations, experiments and a phenomenological description.Comment: Submitted to PRB, RevTeX format, 28 pages and 13 figures, figures in
postscript format are available at http://www.tp.umu.se/~holmlund/papers.htm
Laser ablation loading of a radiofrequency ion trap
The production of ions via laser ablation for the loading of radiofrequency
(RF) ion traps is investigated using a nitrogen laser with a maximum pulse
energy of 0.17 mJ and a peak intensity of about 250 MW/cm^2. A time-of-flight
mass spectrometer is used to measure the ion yield and the distribution of the
charge states. Singly charged ions of elements that are presently considered
for the use in optical clocks or quantum logic applications could be produced
from metallic samples at a rate of the order of magnitude 10^5 ions per pulse.
A linear Paul trap was loaded with Th+ ions produced by laser ablation. An
overall ion production and trapping efficiency of 10^-7 to 10^-6 was attained.
For ions injected individually, a dependence of the capture probability on the
phase of the RF field has been predicted. In the experiment this was not
observed, presumably because of collective effects within the ablation plume.Comment: submitted to Appl. Phys. B., special issue on ion trappin
Cold atoms in a high-Q ring-cavity
We report the confinement of large clouds of ultra-cold 85-Rb atoms in a
standing-wave dipole trap formed by the two counter-propagating modes of a
high-Q ring-cavity. Studying the properties of this trap we demonstrate loading
of higher-order transverse cavity modes and excite recoil-induced resonances.Comment: 4 pages, 4 figure
Helicity Analysis of Semileptonic Hyperon Decays Including Lepton Mass Effects
Using the helicity method we derive complete formulas for the joint angular
decay distributions occurring in semileptonic hyperon decays including lepton
mass and polarization effects. Compared to the traditional covariant
calculation the helicity method allows one to organize the calculation of the
angular decay distributions in a very compact and efficient way. In the
helicity method the angular analysis is of cascade type, i.e. each decay in the
decay chain is analyzed in the respective rest system of that particle. Such an
approach is ideally suited as input for a Monte Carlo event generation program.
As a specific example we take the decay () followed by the nonleptonic decay for which we show a few examples of decay distributions which are
generated from a Monte Carlo program based on the formulas presented in this
paper. All the results of this paper are also applicable to the semileptonic
and nonleptonic decays of ground state charm and bottom baryons, and to the
decays of the top quark.Comment: Published version. 40 pages, 11 figures included in the text. Typos
corrected, comments added, references added and update
Instability of vortex array and transitions to turbulent states in rotating helium II
We consider superfluid helium inside a container which rotates at constant
angular velocity and investigate numerically the stability of the array of
quantized vortices in the presence of an imposed axial counterflow. This
problem was studied experimentally by Swanson {\it et al.}, who reported
evidence of instabilities at increasing axial flow but were not able to explain
their nature. We find that Kelvin waves on individual vortices become unstable
and grow in amplitude, until the amplitude of the waves becomes large enough
that vortex reconnections take place and the vortex array is destabilized. The
eventual nonlinear saturation of the instability consists of a turbulent tangle
of quantized vortices which is strongly polarized. The computed results compare
well with the experiments. Finally we suggest a theoretical explanation for the
second instability which was observed at higher values of the axial flow
Critical Dynamics of Magnets
We review our current understanding of the critical dynamics of magnets above
and below the transition temperature with focus on the effects due to the
dipole--dipole interaction present in all real magnets. Significant progress in
our understanding of real ferromagnets in the vicinity of the critical point
has been made in the last decade through improved experimental techniques and
theoretical advances in taking into account realistic spin-spin interactions.
We start our review with a discussion of the theoretical results for the
critical dynamics based on recent renormalization group, mode coupling and spin
wave theories. A detailed comparison is made of the theory with experimental
results obtained by different measuring techniques, such as neutron scattering,
hyperfine interaction, muon--spin--resonance, electron--spin--resonance, and
magnetic relaxation, in various materials. Furthermore we discuss the effects
of dipolar interaction on the critical dynamics of three--dimensional isotropic
antiferromagnets and uniaxial ferromagnets. Special attention is also paid to a
discussion of the consequences of dipolar anisotropies on the existence of
magnetic order and the spin--wave spectrum in two--dimensional ferromagnets and
antiferromagnets. We close our review with a formulation of critical dynamics
in terms of nonlinear Langevin equations.Comment: Review article (154 pages, figures included
Vortex dynamics for two-dimensional XY models
Two-dimensional XY models with resistively shunted junction (RSJ) dynamics
and time dependent Ginzburg-Landau (TDGL) dynamics are simulated and it is
verified that the vortex response is well described by the Minnhagen
phenomenology for both types of dynamics. Evidence is presented supporting that
the dynamical critical exponent in the low-temperature phase is given by
the scaling prediction (expressed in terms of the Coulomb gas temperature
and the vortex renormalization given by the dielectric constant
) both for RSJ and TDGL
and that the nonlinear IV exponent a is given by a=z+1 in the low-temperature
phase. The results are discussed and compared with the results of other recent
papers and the importance of the boundary conditions is emphasized.Comment: 21 pages including 15 figures, final versio
Weakly-Bound Three-Body Systems with No Bound Subsystems
We investigate the domain of coupling constants which achieve binding for a
3-body system, while none of the 2-body subsystems is bound. We derive some
general properties of the shape of the domain, and rigorous upper bounds on its
size, using a Hall--Post decomposition of the Hamiltonian. Numerical
illustrations are provided in the case of a Yukawa potential, using a simple
variational method.Comment: gzipped ps with 11 figures included. To appear in Phys. Rev.
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