21,419 research outputs found
Stability Limits in Resonant Planetary Systems
The relationship between the boundaries for Hill and Lagrange stability in
orbital element space is modified in the case of resonantly interacting
planets. Hill stability requires the ordering of the planets to remain constant
while Lagrange stability also requires all planets to remain bound to the
central star. The Hill stability boundary is defined analytically, but no
equations exist to define the Lagrange boundary, so we perform numerical
experiments to estimate the location of this boundary. To explore the effect of
resonances, we consider orbital element space near the conditions in the HD
82943 and 55 Cnc systems. Previous studies have shown that, for non-resonant
systems, the two stability boundaries are nearly coincident. However the Hill
stability formula are not applicable to resonant systems, and our investigation
shows how the two boundaries diverge in the presence of a mean-motion
resonance, while confirming that the Hill and Lagrange boundaries are similar
otherwise. In resonance the region of stability is larger than the domain
defined by the analytic formula for Hill stability. We find that nearly all
known resonant interactions currently lie in this extra stable region, i.e.
where the orbits would be unstable according to the non-resonant Hill stability
formula. This result bears on the dynamical packing of planetary systems,
showing how quantifying planetary systems' dynamical interactions (such as
proximity to the Hill-stability boundary) provides new constraints on planet
formation models.Comment: 13 pages, 3 figures, 2 tables, accepted for publication in ApJ
Letters. A version with full resolution figures is available at
http://www.lpl.arizona.edu/~rory/research/xsp/resstab.pd
The Double Bind of Redevelopment: Camden During Receivership
This working paper finds that successful redevelopment efforts in Camden, New Jersey, under state receivership were able to build on groups' existing capacities and their past work in neighborhoods, were marked by more effective participatory dynamics and the limited use of eminent domain, and benefited from good relationships with the State of New Jersey and with private-sector partners. It concludes that attempts to build public capacity to revitalize cities may need to be complemented by efforts to build civic capacity, or the ability to solve problems in coordination with major partners
Empathy
After defining empathy, discussing its measurement, and offering an example of empathy in practice, we present the results of an updated meta-analysis of the relation between empathy and psychotherapy outcome. Results indicated that empathy is a moderately strong predictor of therapy outcome: mean weighted r = .31 ( p < .001; 95% confidence interval: .28 –.34), for 59 independent samples and 3599 clients. Although the empathy-outcome relation held equally for different theoretical orientations, there was considerable nonrandom variability. Client and observer perceptions of therapist empathy predicted outcomes better than therapist perceptions of empathic accuracy measures, and the relation was strongest for less experienced therapists. We conclude with practice recommendations, including endorsing the different forms that empathy may take in therapy
Quantum signal transmission through a single-qubit chain
A system of a two-level atom of an impurity (qubit) inserted into a periodic
chain coupled to the continuum is studied with the use of the effective
non-Hermitian Hamiltonian. Exact solutions are derived for the quasistationary
eigenstates, their complex energies, and transport properties. Due to the
presence of the qubit, two long-lived states corresponding to the ground and
excited states of the qubit emerge outside the Bloch energy band. These states
remain essentially localized at the qubit even in the limit of sufficiently
strong coupling between the chain and the environment when the super-radiant
states are formed. The transmission through the chain is studied as a function
of the continuum coupling strength and the chain-qubit coupling; the perfect
resonance transmission takes place through isolated resonances at weak and
strong continuum coupling, while the transmission is lowered in the
intermediate regime.Comment: In this version we added the case of large N and the case when the
excitation energy of bare qubit is below the band boundary of the bare chain.
The captions to some figures are modified. Some new references are adde
A cost-benefit analysis of pathways to work for new and repeat incapacity benefits claimants
This latest research forms part of a comprehensive independent evaluation of Pathways to Work. The report is based on a cost-benefit analysis conducted by a consortium of researchers from the Institute for Fiscal Studies, the University of Maryland, Baltimore County and the Policy Studies Institute. It examines whether the financial benefits from Pathways are larger or smaller than its costs and the generalisability of some of the quantitative findings. The estimates of costs and benefits relate to new and repeat incapacity benefits claimants in the seven original Jobcentre Plus districts. The overall findings provide a favourable impression of the financial benefits of the Pathways to Work for new and repeat incapacity benefits claimants, for the Exchequer and hence, for society as a whole
Why is CPT fundamental?
G. L\"uders and W. Pauli proved the theorem based on
Lagrangian quantum field theory almost half a century ago. R. Jost gave a more
general proof based on ``axiomatic'' field theory nearly as long ago. The
axiomatic point of view has two advantages over the Lagrangian one. First, the
axiomatic point of view makes clear why is fundamental--because
it is intimately related to Lorentz invariance. Secondly, the axiomatic proof
gives a simple way to calculate the transform of any
relativistic field without calculating , and
separately and then multiplying them. The purpose of this
pedagogical paper is to ``deaxiomatize'' the theorem by
explaining it in a few simple steps. We use theorems of distribution theory and
of several complex variables without proof to make the exposition elementary.Comment: 17 pages, no figure
The Cocaine Cartel\u27s Best Kept Secret…The Black Market Peso Exchange; The Going Is Good, But For How Long, And At What price?
The date is July 2, 1991, piled upon rectangular tables are stacks of United States dollars
Topological Aspects of Spin and Statistics in Nonlinear Sigma Models
We study the purely topological restrictions on allowed spin and statistics
of topological solitons in nonlinear sigma models. Taking as space the
connected -manifold , and considering nonlinear sigma models with the
connected manifold as target space, topological solitons are given by
elements of . Any topological soliton determines
a quotient \Stat_n(X,\alpha) of the group of framed braids on , such that
choices of allowed statistics for solitons of type are given by
unitary representations of \Stat_n(X,\alpha) when solitons are present.
In particular, when , as in the nonlinear sigma model with Hopf
term, and is a generator, we compute that
\Stat_n(\R^2,\alpha) = \Z, while \Stat_n(S^2,\alpha) = \Z_{2n}. It follows
that phase for interchanging two solitons of type on
must satisfy the constraint , , when such
solitons are present.Comment: 14 page
El Secreto Mas Guardado De Los Carteles De la Cocaina…El Intercanbio Del Peso En El Marcado Negro; El Negocio Es Bueno, Pero ἱPor Cuanto Tiempo, y A Que\u27 Precio?
La fecha es el 2 de julio de 1991, amontonadas sobre las mesas rectangulares se encuentran pilas de d6lares
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