3,407 research outputs found
Folly to the Greeks: Good Reasons to Give up Reason
A discussion of why a strong doctrine of 'reason' may not be worth sustaining in the face of modern scientific speculation, and the difficulties this poses for scientific rationality, together with comments on the social understanding of religion, and why we might wish to transcend common sense
Dynamics, dephasing and clustering of impurity atoms in Bose-Einstein condensates
We investigate the influence of a Bose-Einstein condensate (BEC) on the
properties of immersed impurity atoms, which are trapped in an optical lattice.
Assuming a weak coupling of the impurity atoms to the BEC, we derive a quantum
master equation for the lattice system. In the special case of fixed impurities
with two internal states the atoms represent a quantum register and the quantum
master equation reproduces the exact evolution of the qubits. We characterise
the qubit dephasing which is caused by the interspecies coupling and show that
the effect of sub- and superdecoherence is observable for realistic
experimental parameters. Furthermore, the BEC phonons mediate an attractive
interaction between the impurities, which has an important impact on their
spatial distribution. If the lattice atoms are allowed to move, there occurs a
sharp transition with the impurities aggregating in a macroscopic cluster at
experimentally achievable temperatures. We also investigate the impact of the
BEC on the transport properties of the impurity atoms and show that a crossover
from coherent to diffusive behaviour occurs with increasing interaction
strength.Comment: 22 pages, 8 figures, some typos correcte
Slavery, welfare and the sixth extinction
Ng’s laudable concern for animal welfare would be welcome to any sensible slave-owner wishing to preserve his investment. What welfarism – for slave-owners and animal husbandmen – fails to call into question is whether we have the right to breed, hold captive and kill animals at all: If it matters, as the widely recognized slogan of ‘Five Freedoms’ suggests, that animals have the chance to live a ‘normal’ life, then more matters than keeping them ‘happy’ in subjection. Their lives – and also the lives of wild things – also deserve respect
Slavery, welfare and the sixth extinction
Ng’s laudable concern for animal welfare would be welcome to any sensible slave-owner wishing to preserve his investment. What welfarism – for slave-owners and animal husbandmen – fails to call into question is whether we have the right to breed, hold captive and kill animals at all: If it matters, as the widely recognized slogan of ‘Five Freedoms’ suggests, that animals have the chance to live a ‘normal’ life, then more matters than keeping them ‘happy’ in subjection. Their lives – and also the lives of wild things – also deserve respect
Heat current rectification and mobility edges
We investigate how the presence of a single-particle mobility edge in a
system can generate strong heat current rectification. Specifically, we study a
quadratic bosonic chain subject to a quasi-periodic potential and coupled at
its boundaries to spin baths of differing temperature. We find that
rectification increases by orders of magnitude depending on the spatial
position in the chain of localized eigenstates above the mobility edge. The
largest enhancements occur when the coupling of one bath to the system is
dominated by a localized eigenstate, while the other bath couples to numerous
delocalized eigenstates. By tuning the parameters of the quasi-periodic
potential it is thus possible to vary the amplitude, and even invert the
direction, of the rectification.Comment: 5+3 pages 4+4 figure
Decoherence of a quantum memory coupled to a collective spin bath
We study the quantum dynamics of a single qubit coupled to a bath of
interacting spins as a model for decoherence in solid state quantum memories.
The spin bath is described by the Lipkin-Meshkov-Glick model and the bath spins
are subjected to a transverse magnetic field. We investigate the qubit
interacting via either an Ising- or an XY-type coupling term to subsets of bath
spins of differing size. The large degree of symmetry of the bath allows us to
find parameter regimes where the initial qubit state is revived at well defined
times after the qubit preparation. These times may become independent of the
bath size for large baths and thus enable faithful qubit storage even in the
presence of strong coupling to a bath. We analyze a large range of parameters
and identify those which are best suited for quantum memories. In general we
find that a small number of links between qubit and bath spins leads to less
decoherence and that systems with Ising coupling between qubit and bath spins
are preferable.Comment: 13 pages, 8 figure
Does International Trump Domestic Trade? The Seed Potato Market in Canada
trade, potato, Agricultural and Food Policy, International Development,
Does International Trump Domestic Trade? The Seed Potato Market in Canada
trade, potato, Canada, Agricultural and Food Policy, International Development, International Relations/Trade,
Density Matrix Renormalization Group in the Heisenberg Picture
In some cases the state of a quantum system with a large number of subsystems
can be approximated efficiently by the density matrix renormalization group,
which makes use of redundancies in the description of the state. Here we show
that the achievable efficiency can be much better when performing density
matrix renormalization group calculations in the Heisenberg picture, as only
the observable of interest but not the entire state is considered. In some
non-trivial cases, this approach can even be exact for finite bond dimensions.Comment: version to appear in PRL, acronyms in title and abstract expanded,
new improved numerical example
Disease Outbreaks and Agricultural Trade: The Case of Potatoes
This study analyzed the impact of PVYn and potato wart disease outbreaks in PEI on the potato industry. These disease outbreaks resulted in the loss of the US seed export market to PEI producers. The effects of the disease outbreaks were mitigated through value-added processing. Price premiums for processed potatoes allowed PEI potato producers to abandon seed exports without incurring losses. Evidence is presented to suggest that other countries have also used this approach when export restrictions were placed on domestic agricultural industries. Policy response to the two disease outbreaks include: i) development of a zones policy that helped to reopen markets into the US; and ii) financial compensation to producers above the minimum levels required under the Seeds Act and Regulations. Implementation of the zones policy had beneficial impacts on the potato industry and is mirrored in other disease outbreaks. In contrast, compensation above minimum requirements may set a costly precedent for future disease outbreaks and may have caused moral hazard problems.disease, trade, potatoes, Canada, food, safety, Agricultural and Food Policy, International Development, International Relations/Trade,
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