2,967 research outputs found
A Search for Time Variation of the Fine Structure Constant
A method offering an order of magnitude sensitivity gain is described for
using quasar spectra to investigate possible time or space variation in the
fine structure constant, alpha. Applying the technique to a sample of 30
absorption systems, spanning redshifts 0.5 < z< 1.6, obtained with the Keck I
telescope, we derive limits on variations in alpha over a wide range of epochs.
For the whole sample Delta(alpha)/alpha = -1.1 +/- 0.4 x 10^{-5}. This
deviation is dominated by measurements at z > 1, where Delta(alpha)/alpha =
-1.9 +/- 0.5 x 10^{-5}. For z < 1, Delta(alpha)/alpha = -0.2 +/- 0.4 x 10^{-5},
consistent with other known constraints. Whilst these results are consistent
with a time-varying alpha, further work is required to explore possible
systematic errors in the data, although careful searches have so far not
revealed any.Comment: 4 pages, 1 figure, accepted for publication in Physical Review
Letter
Order parameter for two-dimensional critical systems with boundaries
Conformal transformations can be used to obtain the order parameter for
two-dimensional systems at criticality in finite geometries with fixed boundary
conditions on a connected boundary. To the known examples of this class (such
as the disk and the infinite strip) we contribute the case of a rectangle. We
show that the order parameter profile for simply connected boundaries can be
represented as a universal function (independent of the criticality model)
raised to the power eta/2. The universal function can be determined from the
Gaussian model or equivalently a problem in two-dimensional electrostatics. We
show that fitting the order parameter profile to the theoretical form gives an
accurate route to the determination of eta. We perform numerical simulations
for the Ising model and percolation for comparison with these analytic
predictions, and apply this approach to the study of the planar rotor model.Comment: 10 pages, 14 figures. Revisions: Removed many typos, improved
presentation of most of the figure
Inverse Spectral-Scattering Problem with Two Sets of Discrete Spectra for the Radial Schroedinger Equation
The Schroedinger equation on the half line is considered with a real-valued,
integrable potential having a finite first moment. It is shown that the
potential and the boundary conditions are uniquely determined by the data
containing the discrete eigenvalues for a boundary condition at the origin, the
continuous part of the spectral measure for that boundary condition, and a
subset of the discrete eigenvalues for a different boundary condition. This
result extends the celebrated two-spectrum uniqueness theorem of Borg and
Marchenko to the case where there is also a continuous spectru
A Correlation Between Galaxy Morphology and MgII Halo Absorption Strength
(Abridged) We compared the quantified morphological properties of 37
intermediate redshift MgII absorption selected galaxies to the properties of
the absorbing halo gas, observed in the spectra of background quasars. The
galaxy morphologies were measured using GIM2D modeling of Hubble Space
Telescope WFPC-2 images and the absorbing gas properties were obtained from
HIRES/Keck and UVES/VLT quasar spectra. We found a 3.1 sigma correlation
between galaxy morphological asymmetries normalized by the quasar-galaxy
projected separations, A/D, and the MgII rest-frame equivalent widths.
Saturation effects cause increased scatter in the relationship with increasing
W_r(2796). We defined a subsample for which the fraction of saturated pixels in
the absorption profiles is f_sat<0.5. The correlation strengthened to 3.3
sigma. We also find a paucity of small morphological asymmetries for galaxies
selected by MgII absorption as compared to those of the general population of
field galaxies, as measured in the Medium Deep Survey. The K-S probability that
the two samples are drawn from the same galaxy population is ruled out at a
99.8% confidence level. The A/D-W_r(2796) correlation suggests a connection
between the processes that perturb galaxies and the quantity of gas in their
halos, normalized by the impact parameter. Since the perturbations are minor,
it is clear that dramatic processes or events are not required for a galaxy to
have an extended halo; the galaxies appear "normal". We suggest that common,
more mild processes that populate halos with gas, such as satellite galaxy
merging, accretion of the local cosmic web, and longer-range galaxy-galaxy
interactions, consequently also induce the observed minor perturbations in the
galaxies.Comment: Accepted for publication in the Astrophysical Journa
Controlling the quantum dynamics of a mesoscopic spin bath in diamond
Understanding and mitigating decoherence is a key challenge for quantum
science and technology. The main source of decoherence for solid-state spin
systems is the uncontrolled spin bath environment. Here, we demonstrate quantum
control of a mesoscopic spin bath in diamond at room temperature that is
composed of electron spins of substitutional nitrogen impurities. The resulting
spin bath dynamics are probed using a single nitrogen-vacancy (NV) centre
electron spin as a magnetic field sensor. We exploit the spin bath control to
dynamically suppress dephasing of the NV spin by the spin bath. Furthermore, by
combining spin bath control with dynamical decoupling, we directly measure the
coherence and temporal correlations of different groups of bath spins. These
results uncover a new arena for fundamental studies on decoherence and enable
novel avenues for spin-based magnetometry and quantum information processing
On a clear day you can see forever : integrating values and skills in sex offender treatment
The topic of sex offender rehabilitation frequently evokes fierce reactions, ranging from strident demands for harsher sentences contrasted with calls for more imaginative and compassionate sentencing options. There seems to be a polarization of positions centred on the question of offenders\u27 moral standing: are they moral strangers or fellow travellers? This fundamental disagreement about offenders\u27 moral status is at the core of a number of independent, although related current practice and research issues confronting the field, namely: (1) risk management versus strength-based treatment approaches; (2) the utility of utilizing individually tailored versus manual-based programmes for offenders; (3) focusing on the technical aspects or therapy as opposed to relationship and therapist factors (what has been called process issues); and (4) the conflict between protecting the community versus promoting the interests of offenders. In this paper I suggest that an approach to sex offender treatment based on a combination of human rights theory (an ethical resource) and strengths-based approaches can help us navigate our way through the above dilemmas in a way that addressees both the needs of offenders and those of the community
Further Evidence for Cosmological Evolution of the Fine Structure Constant
We describe the results of a search for time variability of the fine
structure constant, alpha, using absorption systems in the spectra of distant
quasars. Three large optical datasets and two 21cm/mm absorption systems
provide four independent samples, spanning 23% to 87% of the age of the
universe. Each sample yields a smaller alpha in the past and the optical sample
shows a 4-sigma deviation: da/a = -0.72 +/- 0.18 x 10^{-5} over the redshift
range 0.5 < z < 3.5. We find no systematic effects which can explain our
results. The only potentially significant systematic effects push da/a towards
positive values, i.e. our results would become more significant were we to
correct for them.Comment: 5 pages, 1 figure. Published in Phys. Rev. Lett. Small changes to
discussion, added an acknowledgement and a referenc
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