14,133 research outputs found
Trend in ice moistening the stratosphere â constraints from isotope data of water and methane
Water plays a major role in the chemistry and radiative budget of the stratosphere. Air enters the stratosphere predominantly in the tropics, where the very low temperatures around the tropopause constrain water vapour mixing ratios to a few parts per million. Observations of stratospheric water vapour show a large positive long-term trend, which can not be explained by change in tropopause temperatures. Trends in the partitioning between vapour and ice of water entering the stratosphere have been suggested to resolve this conundrum. We present measurements of stratospheric H_(2)O, HDO, CH_4 and CH_(3)D in the period 1991â2007 to evaluate this hypothesis. Because of fractionation processes during phase changes, the hydrogen isotopic composition of H_(2)O is a sensitive indicator of changes in the partitioning of vapour and ice. We find that the seasonal variations of H_(2)O are mirrored in the variation of the ratio of HDO to H_(2)O with a slope of the correlation consistent with water entering the stratosphere mainly as vapour. The variability in the fractionation over the entire observation period is well explained by variations in H_(2)O. The isotopic data allow concluding that the trend in ice arising from particulate water is no more than (0.01±0.13) ppmv/decade in the observation period. Our observations suggest that between 1991 and 2007 the contribution from changes in particulate water transported through the tropopause plays only a minor role in altering in the amount of water entering the stratosphere
Optical-Model Description of Time-Reversal Violation
A time-reversal-violating spin-correlation coefficient in the total cross
section for polarized neutrons incident on a tensor rank-2 polarized target is
calculated by assuming a time-reversal-noninvariant, parity-conserving
``five-fold" interaction in the neutron-nucleus optical potential. Results are
presented for the system for neutron incident energies
covering the range 1--20 MeV. From existing experimental bounds, a strength of
keV is deduced for the real and imaginary parts of the five-fold
term, which implies an upper bound of order on the relative -odd
strength when compared to the central real optical potential.Comment: 11 pages (Revtex
Defendants with intellectual disability and autism spectrum conditions the perspective of clinicians working across three jurisdictions
The treatment of vulnerable defendants by criminal justice systems or correctional systems varies within and between countries. The purpose of this paper is to examine three legal jurisdictions â New South Wales in Australia; Norway; England and Wales â to understand the extent of variation in practice within the court systems for defendants with intellectual disabilities (ID) and/or autism spectrum conditions (ASC). Two of the jurisdictions had a process for screening in place, either in police custody or at court, but this was not universally implemented across each jurisdiction. All three jurisdictions had a process for
supporting vulnerable defendants through the legal system. Across the three jurisdictions, there was variation in disposal options from a mandatory care setting to hospital treatment to a custodial sentence for serious offences. This variation requires further international exploration to ensure the rights of defendants with ID or ASC are understood and safeguarde
Aql X-1 in Outburst and Quiescence
We present photometry and spectroscopy of the soft x-ray transient Aql X-1.
Optical photometry during an active state shows a strong (0.6 mag peak-to-peak)
modulation at a period of 19 hours. Infrared (K'-band) photometry during a
quiescent state limits any ellipsoidal variations to <0.07 mag (peak-to-peak),
which implies an inclination i<31 (90% limit). Spectroscopy in a quiescent
state shows at most very small radial velocity variations, which implies a very
low inclination of i<12 (90% limit). The low inclination is rather unexpected
given the large photometric modulation seen in the active state. The upper
limit to the equivalent width of the anomalous Li 6707A line is <0.3A, which is
similar to the measured strength of this line in several other x-ray
transients.Comment: Accepted for publication in ApJ, 12 pages, 5 figure
Holography in asymptotically flat space-times and the BMS group
In a previous paper (hep-th/0306142) we have started to explore the
holographic principle in the case of asymptotically flat space-times and
analyzed in particular different aspects of the Bondi-Metzner-Sachs (BMS)
group, namely the asymptotic symmetry group of any asymptotically flat
space-time. We continue this investigation in this paper. Having in mind a
S-matrix approach with future and past null infinity playing the role of
holographic screens on which the BMS group acts, we connect the IR sectors of
the gravitational field with the representation theory of the BMS group. We
analyze the (complicated) mapping between bulk and boundary symmetries pointing
out differences with respect to the AdS/CFT set up. Finally we construct a BMS
phase space and a free hamiltonian for fields transforming w.r.t BMS
representations. The last step is supposed to be an explorative investigation
of the boundary data living on the degenerate null manifold at infinity.Comment: 31 pages, several changes in section 3 and 7 and references update
A Grassmann integral equation
The present study introduces and investigates a new type of equation which is
called Grassmann integral equation in analogy to integral equations studied in
real analysis. A Grassmann integral equation is an equation which involves
Grassmann integrations and which is to be obeyed by an unknown function over a
(finite-dimensional) Grassmann algebra G_m. A particular type of Grassmann
integral equations is explicitly studied for certain low-dimensional Grassmann
algebras. The choice of the equation under investigation is motivated by the
effective action formalism of (lattice) quantum field theory. In a very general
setting, for the Grassmann algebras G_2n, n = 2,3,4, the finite-dimensional
analogues of the generating functionals of the Green functions are worked out
explicitly by solving a coupled system of nonlinear matrix equations. Finally,
by imposing the condition G[{\bar\Psi},{\Psi}] = G_0[{\lambda\bar\Psi},
{\lambda\Psi}] + const., 0<\lambda\in R (\bar\Psi_k, \Psi_k, k=1,...,n, are the
generators of the Grassmann algebra G_2n), between the finite-dimensional
analogues G_0 and G of the (``classical'') action and effective action
functionals, respectively, a special Grassmann integral equation is being
established and solved which also is equivalent to a coupled system of
nonlinear matrix equations. If \lambda \not= 1, solutions to this Grassmann
integral equation exist for n=2 (and consequently, also for any even value of
n, specifically, for n=4) but not for n=3. If \lambda=1, the considered
Grassmann integral equation has always a solution which corresponds to a
Gaussian integral, but remarkably in the case n=4 a further solution is found
which corresponds to a non-Gaussian integral. The investigation sheds light on
the structures to be met for Grassmann algebras G_2n with arbitrarily chosen n.Comment: 58 pages LaTeX (v2: mainly, minor updates and corrections to the
reference section; v3: references [4], [17]-[21], [39], [46], [49]-[54],
[61], [64], [139] added
- âŠ