168 research outputs found
Urban planning law in Liberia: the case for a transformational approach
This article discusses the need for a fundamental rethinking of urban planning in Liberia with special reference to Monrovia, the capital. Liberia is a post-conflict country and is facing a multitude of problems. One is the very rapid urbanisation of the country. Well over 50% of the population live in urban areas, and over one million peopleâone third of the populationâlive in Monrovia, for the most part in informal âillegalâ settlements with few facilities. Despite land issues being acknowledged as in need of being tackled as a matter of urgency, little has been done by the Johnson-Sirleaf government since it came to power in 2006. What is needed and what this article argues for is a plan for the development of Monrovia based on the Right to the City with residents given clear rights to land and to participate in the governance of their city. The approach is denominated as a transformational one, taking its inspiration from van der Waltâs approach set out in his Property in the Margins. The need for and the outline of an Urban Transformation Act are set out in the article which concludes with a warning that it cannot be supposed that the residents of Monrovia will continue indefinitely to put up with their very poor living conditions
The trajectory of maternal and paternal fatigue and factors associated with fatigue across the transition to parenthood
BackgroundFatigue is prevalent in new parents and is associated with poorer functional performance and cognitive functioning. This can be particularly detrimental during the transition to parenthood when parents are adapting to new roles and demands. Examining the course of fatigue and related factors can provide important avenues for intervention and prevention.MethodsIn this longitudinal study, we assessed fatigue and its correlates in 108 mother/father couples. Multilevel modelling examined the prevalence and trajectory of fatigue across the transition to parenthood, as well as factors associated with postâpartum fatigue. Parents completed measures of fatigue, prenatal stress, depression and health, and postânatal parental sleep quality, infant sleep duration, and infant negativity.ResultsMothers' and fathers' fatigue increased following the birth of their infant and remained at high levels. Poor sleep quality, stress, and depression were associated with maternal and paternal fatigue, while infant characteristics were more strongly associated with maternal fatigue. Prenatal depressive symptoms, parental sleep quality, infant sleep duration, and the interaction of gender by prenatal fatigue predicted postânatal fatigue in our model.ConclusionOur results highlight the need for health professionals to educate new parents about fatigue and its management beyond the prenatal period. As correlates of fatigue for mothers and fathers differ, we need to expand our understanding of paternal fatigue and develop interventions tailored to their unique experiences.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110817/1/cp12048.pd
Laser cooling and control of excitations in superfluid helium
Superfluidity is an emergent quantum phenomenon which arises due to strong
interactions between elementary excitations in liquid helium. These excitations
have been probed with great success using techniques such as neutron and light
scattering. However measurements to-date have been limited, quite generally, to
average properties of bulk superfluid or the driven response far out of thermal
equilibrium. Here, we use cavity optomechanics to probe the thermodynamics of
superfluid excitations in real-time. Furthermore, strong light-matter
interactions allow both laser cooling and amplification of the thermal motion.
This provides a new tool to understand and control the microscopic behaviour of
superfluids, including phonon-phonon interactions, quantised vortices and
two-dimensional quantum phenomena such as the Berezinskii-Kosterlitz-Thouless
transition. The third sound modes studied here also offer a pathway towards
quantum optomechanics with thin superfluid films, including femtogram effective
masses, high mechanical quality factors, strong phonon-phonon and phonon-vortex
interactions, and self-assembly into complex geometries with sub-nanometre
feature size.Comment: 6 pages, 4 figures. Supplementary information attache
Minimum requirements for feedback enhanced force sensing
The problem of estimating an unknown force driving a linear oscillator is
revisited. When using linear measurement, feedback is often cited as a
mechanism to enhance bandwidth or sensitivity. We show that as long as the
oscillator dynamics are known, there exists a real-time estimation strategy
that reproduces the same measurement record as any arbitrary feedback protocol.
Consequently some form of nonlinearity is required to gain any advantage beyond
estimation alone. This result holds true in both quantum and classical systems,
with non-stationary forces and feedback, and in the general case of
non-Gaussian and correlated noise. Recently, feedback enhanced incoherent force
sensing has been demonstrated [Nat. Nano. \textbf{7}, 509 (2012)], with the
enhancement attributed to a feedback induced modification of the mechanical
susceptibility. As a proof-of-principle we experimentally reproduce this result
through straightforward filtering.Comment: 5 pages + 2 pages of Supplementary Informatio
Thin film superfluid optomechanics
Excitations in superfluid helium represent attractive mechanical degrees of
freedom for cavity optomechanics schemes. Here we numerically and analytically
investigate the properties of optomechanical resonators formed by thin films of
superfluid He covering micrometer-scale whispering gallery mode cavities.
We predict that through proper optimization of the interaction between film and
optical field, large optomechanical coupling rates kHz
and single photon cooperativities are achievable. Our analytical model
reveals the unconventional behaviour of these thin films, such as thicker and
heavier films exhibiting smaller effective mass and larger zero point motion.
The optomechanical system outlined here provides access to unusual regimes such
as and opens the prospect of laser cooling a liquid into its
quantum ground state.Comment: 18 pages, 6 figure
Microphotonic Forces From Superfluid Flow
In cavity optomechanics, radiation pressure and photothermal forces are
widely utilized to cool and control micromechanical motion, with applications
ranging from precision sensing and quantum information to fundamental science.
Here, we realize an alternative approach to optical forcing based on superfluid
flow and evaporation in response to optical heating. We demonstrate optical
forcing of the motion of a cryogenic microtoroidal resonator at a level of 1.46
nN, roughly one order of magnitude larger than the radiation pressure force. We
use this force to feedback cool the motion of a microtoroid mechanical mode to
137 mK. The photoconvective forces demonstrated here provide a new tool for
high bandwidth control of mechanical motion in cryogenic conditions, and have
the potential to allow efficient transfer of electromagnetic energy to motional
kinetic energy.Comment: 5 pages, 6 figure
Photon echo quantum memories in inhomogeneously broadened two level atoms
Here we propose a solid-state quantum memory that does not require spectral
holeburning, instead using strong rephasing pulses like traditional photon echo
techniques. The memory uses external broadening fields to reduce the optical
depth and so switch off the collective atom-light interaction when desired. The
proposed memory should allow operation with reasonable efficiency in a much
broader range of material systems, for instance Er3+ doped crystals which have
a transition at 1.5 um. We present analytic theory supported by numerical
calculations and initial experiments.Comment: 7 pages, 8 figure
Optomechanical magnetometry with a macroscopic resonator
We demonstrate a centimeter-scale optomechanical magnetometer based on a
crystalline whispering gallery mode resonator. The large size of the resonator
allows high magnetic field sensitivity to be achieved in the hertz to kilohertz
frequency range. A peak sensitivity of 131 pT per root Hz is reported, in a
magnetically unshielded non-cryogenic environment and using optical power
levels beneath 100 microWatt. Femtotesla range sensitivity may be possible in
future devices with further optimization of laser noise and the physical
structure of the resonator, allowing applications in high-performance
magnetometry
Coherent vortex dynamics in a strongly-interacting superfluid on a silicon chip
Two-dimensional superfluidity and quantum turbulence are directly connected
to the microscopic dynamics of quantized vortices. However, surface effects
have prevented direct observations of coherent vortex dynamics in
strongly-interacting two-dimensional systems. Here, we overcome this challenge
by confining a two-dimensional droplet of superfluid helium at microscale on
the atomically-smooth surface of a silicon chip. An on-chip optical microcavity
allows laser-initiation of vortex clusters and nondestructive observation of
their decay in a single shot. Coherent dynamics dominate, with thermal vortex
diffusion suppressed by six orders-of-magnitude. This establishes a new on-chip
platform to study emergent phenomena in strongly-interacting superfluids, test
astrophysical dynamics such as those in the superfluid core of neutron stars in
the laboratory, and construct quantum technologies such as precision inertial
sensors.Comment: Main text - 12 pages, 4 figures. Supplementary materials - 25 pages,
13 figure
The first legal mortgagor: a consumer without adequate protection?
This article contends that the UK governmentâs attempt to create a well-functioning consumer credit market will be undermined if it fails to reform the private law framework relating to the first legal mortgage. Such agreements are governed by two distinct regulatory regimes that are founded upon very different conceptions of the mortgagor. The first, the regulation of financial services overseen by the Financial Conduct Authority, derives from public law and is founded upon a conception of the mortgagor as âconsumerâ. The other is land law, private law regulation implemented by the judiciary and underpinned by a conception of the mortgagor as âlandownerâ. Evidence suggests that the operation of these two regimes prevents mortgagors from receiving fair and consistent treatment. The current reform of financial services regulation therefore will change only one part of this governance regime and will leave mortgagors heavily reliant upon a regulator that still has to prove itself. What this article argues is that reform of the rules of private law must also be undertaken with the aim of initiating a paradigm shift in the conception of the mortgagor from âlandownerâ to âconsumerâ. Cultural shifts of this kind take time but the hope is that this conceptual transformation will occur in time to deter the predicted rise in mortgage possessions
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