3,375 research outputs found
Tides and the Evolution of Planetary Habitability
Tides raised on a planet by its host star's gravity can reduce a planet's
orbital semi-major axis and eccentricity. This effect is only relevant for
planets orbiting very close to their host stars. The habitable zones of
low-mass stars are also close-in and tides can alter the orbits of planets in
these locations. We calculate the tidal evolution of hypothetical terrestrial
planets around low-mass stars and show that tides can evolve planets past the
inner edge of the habitable zone, sometimes in less than 1 billion years. This
migration requires large eccentricities (>0.5) and low-mass stars (<0.35
M_Sun). Such migration may have important implications for the evolution of the
atmosphere, internal heating and the Gaia hypothesis. Similarly, a planet
detected interior to the habitable zone could have been habitable in the past.
We consider the past habitability of the recently-discovered, ~5 M_Earth
planet, Gliese 581 c. We find that it could have been habitable for reasonable
choices of orbital and physical properties as recently as 2 Gyr ago. However,
when we include constraints derived from the additional companions, we see that
most parameter choices that predict past habitability require the two inner
planets of the system to have crossed their mutual 3:1 mean motion resonance.
As this crossing would likely have resulted in resonance capture, which is not
observed, we conclude that Gl 581 c was probably never habitable.Comment: 31 pages, 10 figures, accepted to Astrobiology. A version with full
resolution figures is available at
http://www.lpl.arizona.edu/~rory/publications/brjg07.pd
Characterizing Multi-planet Systems with Classical Secular Theory
Classical secular theory can be a powerful tool to describe the qualitative
character of multi-planet systems and offer insight into their histories. The
eigenmodes of the secular behavior, rather than current orbital elements, can
help identify tidal effects, early planet-planet scattering, and dynamical
coupling among the planets, for systems in which mean-motion resonances do not
play a role. Although tidal damping can result in aligned major axes after all
but one eigenmode have damped away, such alignment may simply be fortuitous. An
example of this is 55 Cancri (orbital solution of Fischer et al., 2008) where
multiple eigenmodes remain undamped. Various solutions for 55 Cancri are
compared, showing differing dynamical groupings, with implications for the
coupling of eccentricities and for the partitioning of damping among the
planets. Solutions for orbits that include expectations of past tidal evolution
with observational data, must take into account which eigenmodes should be
damped, rather than expecting particular eccentricities to be near zero.
Classical secular theory is only accurate for low eccentricity values, but
comparison with other results suggests that it can yield useful qualitative
descriptions of behavior even for moderately large eccentricity values, and may
have advantages for revealing underlying physical processes and, as large
numbers of new systems are discovered, for triage to identify where more
comprehensive dynamical studies should have priority.Comment: Published in Celestial Mechanics and Dynamical Astronomy, 25 pages,
10 figure
Spin Observables in Antilambda-Lambda Production from Antiproton-Proton Annihilation with a Transverse Inital State Polarization
The formalism describing the scattering of two spin-1/2 objects is reviewed
for the case of antilambda-lambda production from antiproton-proton
annihilation. It is shown that an experiment utilizing a transverse target
polarization can, in principle, completely determine the spin structure of the
reaction. Additional measurements, even those using both beam and target
polarizations, would not be sensitive to any additional spin dynamics. Thus,
the transverse target polarization allows access to the complete set of spin
observables, not just the subset upon which the literature has previously
focused. This discussion is especially relevant in light of the data collected
by PS185/3 at LEAR.Comment: 7 pages, no figure
Dissociation cross sections of ground-state and excited charmonia with light mesons in the quark model
We present numerical results for the dissociation cross sections of
ground-state, orbitally- and radially-excited charmonia in collisions with
light mesons. Our results are derived using the nonrelativistic quark model, so
all parameters are determined by fits to the experimental meson spectrum.
Examples of dissociation into both exclusive and inclusive final states are
considered. The dissociation cross sections of several C=(+) charmonia may be
of considerable importance for the study of heavy ion collisions, since these
states are expected to be produced more copiously than the J/psi. The relative
importance of the productions of ground-state and orbitally-excited charmed
mesons in a pion-charmonium collision is demonstrated through the -dependent charmonium dissociation cross sections.Comment: 9 pages, 8 figure
Constraints on spin observables in antiproton-proton to antiLambda-Lambda
It is recalled that spin-observables in the strangeness-exchange reaction
are not independent but are related to
each other by simple algebraic relations. This provides constraints on the
existing data on polarization and spin-correlation coefficients, and also on
the forthcoming data obtained using a polarized proton target.Comment: RevTex, 9 page
Magnetic characterization of superparamagnetic nanoparticles pulled through model membranes
BACKGROUND: To quantitatively compare in-vitro and in vivo membrane transport studies of targeted delivery, one needs characterization of the magnetically-induced mobility of superparamagnetic iron oxide nanoparticles (SPION). Flux densities, gradients, and nanoparticle properties were measured in order to quantify the magnetic force on the SPION in both an artificial cochlear round window membrane (RWM) model and the guinea pig RWM. METHODS: Three-dimensional maps were created for flux density and magnetic gradient produced by a 24-well casing of 4.1 kilo-Gauss neodymium-iron-boron (NdFeB) disc magnets. The casing was used to pull SPION through a three-layer cell culture RWM model. Similar maps were created for a 4 inch (10.16 cm) cube 48 MGOe NdFeB magnet used to pull polymeric-nanoparticles through the RWM of anesthetized guinea pigs. Other parameters needed to compute magnetic force were nanoparticle and polymer properties, including average radius, density, magnetic susceptibility, and volume fraction of magnetite. RESULTS: A minimum force of 5.04 × 10(-16 )N was determined to adequately pull nanoparticles through the in-vitro model. For the guinea pig RWM, the magnetic force on the polymeric nanoparticles was 9.69 × 10(-20 )N. Electron microscopy confirmed the movement of the particles through both RWM models. CONCLUSION: As prospective carriers of therapeutic substances, polymers containing superparamagnetic iron oxide nanoparticles were succesfully pulled through the live RWM. The force required to achieve in vivo transport was significantly lower than that required to pull nanoparticles through the in-vitro RWM model. Indeed very little force was required to accomplish measurable delivery of polymeric-SPION composite nanoparticles across the RWM, suggesting that therapeutic delivery to the inner ear by SPION is feasible
The future of marine fisheries management and conservation in the United Kingdom: Lessons learnt from over 100 years of biased policy
Marine wild-capture fisheries depend on the capacity of the ocean to provide a flow of harvestable resources to
sustain the industry. Paradoxically, conventional fishing often undermines these resources by degrading the
environment and overexploiting fish stocks. Many UK fisheries have declined for over a century due to a biased
focus on their social-economic value and lack of recognition that they are social-ecological systems and need to
be managed as such. With the UK’s recent transition to an independent coastal state, the Fisheries Act (2020) and
associated Joint Fisheries Statement provide an opportunity to correct this. Focusing on the ecological foundations, a more sustainable future for UK fisheries may be achieved by: (1) implementing a conservative quota
setting system based on Maximum Sustainable Yield (MSY), defined as that which would occur when the biomass
of a population of the target species is at 50% of that estimated at carrying capacity, to set catch limits rather
than targets. The biomass of fish stocks should be allowed to regenerate to a minimum of 120% of that which will
achieve MSY to provide a buffer against the uncertainty in ecological response to climate change. (2) Fishing
capacity should be reduced while redistributing a greater share of the quota to sectors of the fleet that are
demonstrably more sustainable; recognising that short term compensation may be required by some to mitigate
the impacts of displaced activity until the benefits of stock recovery are realised. (3) Greater restrictions should
be applied to ensure the most damaging fishing techniques (e.g. bottom trawling and dredging) are prohibited as
appropriate in the network of marine protected areas. Protection should be enforced to promote the regeneration
of degraded habitats and restoration of fish populations to help achieve the objectives as set out in the Ac
Eigenvalue bounds for polynomial central potentials in d dimensions
If a single particle obeys non-relativistic QM in R^d and has the Hamiltonian
H = - Delta + f(r), where f(r)=sum_{i = 1}^{k}a_ir^{q_i}, 2\leq q_i < q_{i+1},
a_i \geq 0P_i =
P_{n\ell}^{(d)}(q_k) and a general approximation formula if P_i =
P_{n\ell}^{(d)}(q_i). For the quantum anharmonic oscillator f(r)=r^2+\lambda
r^{2m},m=2,3,... in d dimension, for example, E = E_{n\ell}^{(d)}(\lambda) is
determined by the algebraic expression
\lambda={1\over \beta}({2\alpha(m-1)\over mE-\delta})^m({4\alpha \over
(mE-\delta)}-{E\over (m-1)}) where \delta={\sqrt{E^2m^2-4\alpha(m^2-1)}} and
\alpha, \beta are constants. An improved lower bound to the lowest eigenvalue
in each angular-momentum subspace is also provided. A comparison with the
recent results of Bhattacharya et al (Phys. Lett. A, 244 (1998) 9) and Dasgupta
et al (J. Phys. A: Math. Theor., 40 (2007) 773) is discussed.Comment: 13 pages, no figure
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