6,462 research outputs found
Scaling forces to asteroid surfaces: The role of cohesion
The scaling of physical forces to the extremely low ambient gravitational
acceleration regimes found on the surfaces of small asteroids is performed.
Resulting from this, it is found that van der Waals cohesive forces between
regolith grains on asteroid surfaces should be a dominant force and compete
with particle weights and be greater, in general, than electrostatic and solar
radiation pressure forces. Based on this scaling, we interpret previous
experiments performed on cohesive powders in the terrestrial environment as
being relevant for the understanding of processes on asteroid surfaces. The
implications of these terrestrial experiments for interpreting observations of
asteroid surfaces and macro-porosity are considered, and yield interpretations
that differ from previously assumed processes for these environments. Based on
this understanding, we propose a new model for the end state of small, rapidly
rotating asteroids which allows them to be comprised of relatively fine
regolith grains held together by van der Waals cohesive forces.Comment: 54 pages, 7 figure
A Pre-Protostellar Core in L1551. II. State of Dynamical and Chemical Evolution
Both analytic and numerical radiative transfer models applied to high
spectral resolution CS and N2H+ data give insight into the evolutionary state
of L1551 MC. This recently discovered pre-protostellar core in L1551 appears to
be in the early stages of dynamical evolution. Line-of-sight infall velocities
of >0.1km/s are needed in the outer regions of L1551 MC to adequately fit the
data. This translates to an accretion rate of ~ 1e-6 Msun/yr, uncertain to
within a factor of 5 owing to unknown geometry. The observed dynamics are not
due to spherically symmetric gravitational collapse and are not consistent with
the standard model of low-mass star formation. The widespread, fairly uniform
CS line asymmetries are more consistent with planar infall. There is modest
evidence for chemical depletion in the radial profiles of CS and C18O
suggesting that L1551 MC is also chemically young. The models are not very
sensitive to chemical evolution. L1551 MC lies within a quiescent region of
L1551 and is evidence for continued star formation in this evolved cloud.Comment: 27 pages, 7 figures, ApJ accepte
Friction and wear of human hair fibres
An experimental study of the tribological properties of hair fibres is reported, and the effect of surface treatment on the evolution of friction and wear during sliding. Specifically, orthogonally crossed fibre/fibre contacts under a compressive normal load over a series of 10,000 cycle studies are investigated. Reciprocating sliding at a velocity of 0.4 mm/s−1, over a track length of 0.8 mm, was performed at 18oC and 40-50% relative humidity. Hair fibres retaining their natural sebum were studied, as well as those stripped of their sebum via hexane cleaning, and hair fibres conditioned using a commercially available product. Surface topography modifications resulting from wear were imaged using scanning electron microscopy and quantified using white light interferometry. Hair fibres that presented sebum or conditioned product at the fibre/fibre junction exhibited initial coefficients of friction at least 25% lower than those that were cleaned with hexane. Coefficients of friction were observed to depend on the directionality of sliding for hexane cleaned hair fibres after sufficient wear cycles that cuticle lifting was present, typically on the order 1,000 cycles. Cuticle flattening was observed for fibre/fibre junctions exposed to 10 mN compressive normal loads, whereas loads of 100 mN introduced substantial cuticle wear and fibre damage
An Evaluation of the Impact of the Social Care Modernisation Programme on the Implementation of Direct Payments London
Domain Coarsening in Systems Far from Equilibrium
The growth of domains of stripes evolving from random initial conditions is
studied in numerical simulations of models of systems far from equilibrium such
as Rayleigh-Benard convection. The scaling of the size of the domains deduced
from the inverse width of the Fourier spectrum is studied for both potential
and nonpotential models. The morphology of the domains and the defect
structures are however quite different in the two cases, and evidence is
presented for a second length scale in the nonpotential case.Comment: 11 pages, RevTeX; 3 uufiles encoded postscript figures appende
X-ray diffraction from shock-loaded polycrystals
X-ray diffraction was demonstrated from shock-compressed polycrystalline
metal on nanosecond time scales. Laser ablation was used to induce shock waves
in polycrystalline foils of Be, 25 to 125 microns thick. A second laser pulse
was used to generate a plasma x-ray source by irradiation of a Ti foil. The
x-ray source was collimated to produce a beam of controllable diameter, and the
beam was directed at the Be sample. X-rays were diffracted from the sample, and
detected using films and x-ray streak cameras. The diffraction angle was
observed to change with shock pressure. The diffraction angles were consistent
with the uniaxial (elastic) and isotropic (plastic) compressions expected for
the loading conditions used. Polycrystalline diffraction will be used to
measure the response of the crystal lattice to high shock pressures and through
phase changes
Active Listening by Hospital Chaplaincy Volunteers: Benefits, Challenges and Good Practice
Active listening (AL) is a communication technique frequently used in counselling. This study explored the feasibility of implementing a ward-based AL intervention for patients by chaplaincy volunteers in the UK National Health Service. Seven focus groups (n=47) included healthcare researchers, lecturers, nurses, patients, AL tutors, active listeners volunteers and chaplaincy volunteers. Acceptability and perceived effectiveness of a patient/volunteer listener intervention were explored. Analysis followed the framework approach. Four themes emerged: (a) Listening as a wellbeing generator; (b) Benefits of AL delivered by volunteers; (c) Spirituality and public perceptions of hospital chaplaincy; (d) Challenges of structured communication techniques in acute care. Participants reported positive attitudes towards the introduction of AL provided by volunteers in acute wards. They shared a common belief that when people are listened to, wellbeing improves through control, choice and empowerment. Patients’ acceptability of the intervention increased if it was delivered by volunteers
The microwave radiometer signature of artificially generated sea foam
Microwave radiometer experiments were undertaken to measure the thermal emission from artificially generated sea foam. This data is used to quantify the physics of emission from the ocean to more accurately retrieve geophysical parameters of interest
- …