8,265 research outputs found
Electron paramagnetic resonance and photochromism of in diamond
The defect in diamond formed by a vacancy surrounded by three
nearest-neighbor nitrogen atoms and one carbon atom,
, is found in of natural diamonds.
Despite being the earliest electron paramagnetic
resonance spectrum observed in diamond, to date no satisfactory simulation of
the spectrum for an arbitrary magnetic field direction has been produced due to
its complexity. In this work, is identified in
-doped synthetic diamond following irradiation and annealing.
The spin Hamiltonian parameters are revised
and used to refine the parameters for ,
enabling the latter to be accurately simulated and fitted for an arbitrary
magnetic field direction. Study of under
excitation with green light indicates charge transfer between
and . It is argued that this charge
transfer is facilitated by direct ionization of ,
an as-yet unobserved charge state of
Improvements and modifications to the NASA microwave signature acquisition system
A user oriented description of the modified and upgraded Microwave Signature Acquisition System is provided. The present configuration of the sensor system and its operating characteristics are documented and a step-by-step operating procedure provides instruction for mounting the antenna truss assembly, readying the system for data acquisition, and for controlling the system during the data collection sequence. The resulting data products are also identified
Few-body resonances of unequal-mass systems with infinite interspecies two-body s-wave scattering length
Two-component Fermi and Bose gases with infinitely large interspecies s-wave
scattering length exhibit a variety of intriguing properties. Among these
are the scale invariance of two-component Fermi gases with equal masses, and
the favorable scaling of Efimov features for two-component Bose gases and
Bose-Fermi mixtures with unequal masses. This paper builds on our earlier work
[D. Blume and K. M. Daily, arXiv:1006.5002] and presents a detailed discussion
of our studies of small unequal-mass two-component systems with infinite
in the regime where three-body Efimov physics is absent. We report on
non-universal few-body resonances. Just like with two-body systems on
resonance, few-body systems have a zero-energy bound state in free space and a
diverging generalized scattering length. Our calculations are performed within
a non-perturbative microscopic framework and investigate the energetics and
structural properties of small unequal-mass two-component systems as functions
of the mass ratio , and the numbers and of heavy and
light atoms. For purely attractive Gaussian two-body interactions, we find that
the and systems exhibit three-body and four-body
resonances at mass ratios and 10.4(2), respectively. The
three- and four-particle systems on resonance are found to be large. This
suggests that the corresponding wave function has relatively small overlap with
deeply-bound dimers, trimers or larger clusters and that the three- and
four-body systems on resonance have a comparatively long lifetime. Thus, it
seems feasible that the features discussed in this paper can be probed
experimentally with present-day technology.Comment: 17 pages, 17 figure
Explosive events associated with a surge
The solar atmosphere contains a wide variety of small-scale transient
features. Here, we explore the inter-relation between some of them such as
surges, explosive events and blinkers via simultaneous spectral and imaging
data taken with the TRACE imager, the SUMER, and CDS spectrometers on board
SoHO, and SVST La Palma. The alignment of all data both in time and solar XY
shows that SUMER line profiles, which are attributed to explosive events, are
due to a surge phenomenon. The surge is triggered, most probably, by one or
more Elerman bombs which are best visible in Halpha +-350 A but were also
registered by TRACE Fe IX/X 171 A and correspond to a strong radiance increase
in the CDS Mg IX 368.07 A line. With the present study we demonstrate that the
division of small-scale transient events into a number of different subgroups,
for instance explosive events, blinkers, spicules, surges or just brightenings,
is ambiguous, implying that the definition of a feature based only on either
spectroscopic or imaging characteristics as well as insufficient spectral and
spatial resolution can be incomplete.Comment: 17 pages, 7 figures, 1 tabl
Example of two different potentials which have practically the same fixed-energy phase shifts
It is shown that the Newton-Sabatier procedure for inverting the fixed-energy
phase shifts for a potential is not an inversion method but a parameter-fitting
procedure. Theoretically there is no guarantee that this procedure is
applicable to the given set of the phase shifts, if it is applicable, there is
no guaran- tee that the potential it produces generates the phase shifts from
which it was reconstructed. Moreover, no generic potential, specifically, no
potential which is not analytic in a neighborhood of the positive real semiaxis
can be reconstructed by the Newton-Sabatier procedure.
A numerical method is given for finding spherically symmetric compactly
supported potentials which produce practically the same set of fixed-energy
phase shifts for all values of angular momentum. Concrete example of such
potentials is given
Generic Constraints on the Relativistic Mean-Field and Skyrme-Hartree-Fock Models from the Pure Neutron Matter Equation of State
We study the nuclear symmetry energy S(rho) and related quantities of nuclear
physics and nuclear astrophysics predicted generically by relativistic
mean-field (RMF) and Skyrme-Hartree-Fock (SHF) models. We establish a simple
prescription for preparing equivalent RMF and SHF parametrizations starting
from a minimal set of empirical constraints on symmetric nuclear matter,
nuclear binding energy and charge radii, enforcing equivalence of their Lorenz
effective masses, and then using the pure neutron matter (PNM) equation of
state (EoS) obtained from ab-initio calculations to optimize the pure isovector
parameters in the RMF and SHF models. We find the resulting RMF and SHF
parametrizations give broadly consistent predictions of the symmetry energy J
and its slope parameter L at saturation density within a tight range of <~2 MeV
and <~6 MeV respectively, but that clear model dependence shows up in the
predictions of higher-order symmetry energy parameters, leading to important
differences in (a) the slope of the correlation between J and L from the
confidence ellipse, (b) the isospin-dependent part of the incompressibility of
nuclear matter K_tau, (c) the symmetry energy at supra-saturation densities,
and (d) the predicted neutron star radii. The model dependence can lead to
about 1-2 km difference in predictions of the neutron star radius given
identical predicted values of J, L and symmetric nuclear matter (SNM)
saturation properties. Allowing the full freedom in the effective masses in
both models leads to constraints of 30<~J<~31.5 MeV, 35<~L<~60 MeV,
-330<~K_tau<~-216 MeV for the RMF model as a whole and 30<~J<~33 MeV, 28<~L<~65
MeV, -420<~K_tau<~-325 MeV for the SHF model as a whole. Notably, given PNM
constraints, these results place RMF and SHF models as a whole at odds with
some constraints on K_tau inferred from giant monopole resonance and neutron
skin experimental results.Comment: 15 pages, 7 figures, 4 table
Scattering Wave Functions at Bound State Poles
The normalisation relation between the bound and scattering S-state wave
functions, extrapolated to the bound state pole, is derived from the
Schroedinger equation. It is shown that, unlike previous work, the result does
not depend on the details of the potential through the corresponding Jost
function but is given uniquely in terms of the binding energy. The
generalisations to higher partial waves and one-dimensional scattering are
given.Comment: 15 pages Latex. No graph
Multichannel Anomaly of the Resonance Pole Parameters Resolved
Inspired by anomalies which the standard scattering matrix pole-extraction
procedures have produced in a mathematically well defined coupled-channel
model, we have developed a new method based solely on the assumption of
partial-wave analyticity. The new method is simple and applicable not only to
theoretical predictions but to the empirical partial-wave data as well. Since
the standard pole-extraction procedures turn out to be the lowest-order term of
the proposed method the anomalies are understood and resolved.Comment: 5 page
Hydrothermal activity lowers trophic diversity in Antarctic sedimented hydrothermal vents
Sedimented hydrothermal vents are those in which hydrothermal fluid vents through sediment and are among the least studied deep-sea ecosystems. We present a combination of microbial and biochemical data to assess trophodynamics between and within hydrothermally active and off-vent areas of the Bransfield Strait (1050–1647 m depth). Microbial composition, biomass and fatty acid signatures varied widely between and within vent and non-vent sites and provided evidence of diverse metabolic activity. Several species showed diverse feeding strategies and occupied different trophic positions in vent and non-vent areas and stable isotope values of consumers were generally not consistent with feeding structure morphology. Niche area and the diversity of microbial fatty acids reflected trends in species diversity and was lowest at the most hydrothermally active site. Faunal utilisation of chemosynthetic activity was relatively limited but was detected at both vent and non-vent sites as evidenced by carbon and sulphur isotopic signatures, suggesting that the hydrothermal activity can affect trophodynamics over a much wider area than previously thought
The gravitational S-matrix
We investigate the hypothesized existence of an S-matrix for gravity, and
some of its expected general properties. We first discuss basic questions
regarding existence of such a matrix, including those of infrared divergences
and description of asymptotic states. Distinct scattering behavior occurs in
the Born, eikonal, and strong gravity regimes, and we describe aspects of both
the partial wave and momentum space amplitudes, and their analytic properties,
from these regimes. Classically the strong gravity region would be dominated by
formation of black holes, and we assume its unitary quantum dynamics is
described by corresponding resonances. Masslessness limits some powerful
methods and results that apply to massive theories, though a continuation path
implying crossing symmetry plausibly still exists. Physical properties of
gravity suggest nonpolynomial amplitudes, although crossing and causality
constrain (with modest assumptions) this nonpolynomial behavior, particularly
requiring a polynomial bound in complex s at fixed physical momentum transfer.
We explore the hypothesis that such behavior corresponds to a nonlocality
intrinsic to gravity, but consistent with unitarity, analyticity, crossing, and
causality.Comment: 46 pages, 10 figure
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