51,784 research outputs found
Universal Amplitude Ratios of The Renormalization Group: Two-Dimensional Tricritical Ising Model
The scaling form of the free-energy near a critical point allows for the
definition of various thermodynamical amplitudes and the determination of their
dependence on the microscopic non-universal scales. Universal quantities can be
obtained by considering special combinations of the amplitudes. Together with
the critical exponents they characterize the universality classes and may be
useful quantities for their experimental identification. We compute the
universal amplitude ratios for the Tricritical Ising Model in two dimensions by
using several theoretical methods from Perturbed Conformal Field Theory and
Scattering Integrable Quantum Field Theory. The theoretical approaches are
further supported and integrated by results coming from a numerical
determination of the energy eigenvalues and eigenvectors of the off-critical
systems in an infinite cylinder.Comment: 61 pages, Latex file, figures in a separate fil
Spectroscopic Confirmation of the Dwarf Galaxies Hydra II and Pisces II and the Globular Cluster Laevens 1
We present Keck/DEIMOS spectroscopy of stars in the recently discovered Milky
Way satellites Hydra II, Pisces II, and Laevens 1. We measured a velocity
dispersion of 5.4 (+3.6 -2.4) km/s for Pisces II, but we did not resolve the
velocity dispersions of Hydra II or Laevens 1. We marginally resolved the
metallicity dispersions of Hydra II and Pisces II but not Laevens 1.
Furthermore, Hydra II and Pisces II obey the luminosity-metallicity relation
for Milky Way dwarf galaxies ( = -2.02 +/- 0.08 and -2.45 +/- 0.07,
respectively), whereas Laevens 1 does not ( = -1.68 +/- 0.05). The
kinematic and chemical properties suggest that Hydra II and Pisces II are dwarf
galaxies, and Laevens 1 is a globular cluster. We determined that two of the
previously observed blue stars near the center of Laevens 1 are not members of
the cluster. A third blue star has ambiguous membership. Hydra II has a radial
velocity = 303.1 +/- 1.4 km/s, similar to the leading arm of the
Magellanic stream. The mass-to-light ratio for Pisces II is 370 (+310 -240)
M_sun/L_sun. It is not among the most dark matter-dominated dwarf galaxies, but
it is still worthy of inclusion in the search for gamma rays from dark matter
self-annihilation.Comment: Accepted to ApJ. v2 has been revised in response to the referee's
repor
Resilience of multi-photon entanglement under losses
We analyze the resilience under photon loss of the bi-partite entanglement
present in multi-photon states produced by parametric down-conversion. The
quantification of the entanglement is made possible by a symmetry of the states
that persists even under polarization-independent losses. We examine the
approach of the states to the set of states with a positive partial transpose
as losses increase, and calculate the relative entropy of entanglement. We find
that some bi-partite distillable entanglement persists for arbitrarily high
losses.Comment: 5 pages, 3 figures, title changed, minor typographic errors correcte
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Pollination services in the UK: how important are honeybees?
Pollination services are known to provide substantial benefits to human populations and agriculture in particular. Although many species are known to provide pollination services, honeybees (Apis mellifera) are often assumed to provide the majority of these services to agriculture. Using data from a range of secondary sources, this study assesses the importance of insect pollinated crops at regional and national scales and investigates the capacity of honeybees to provide optimal pollination services to UK agriculture. The findings indicate that insect pollinated crops have become increasingly important in UK crop agriculture and, as of 2007, accounted for 20% of UK cropland and 19% of total farmgate crop value. Analysis of honeybee hive numbers indicates that current UK populations are only capable of supplying 34% of pollination service demands even under favourable assumptions, falling from 70% in 1984. In spite of this decline, insect pollinated crop yields have risen by an average of 54% since 1984, casting doubt on long held beliefs that honeybees provide the majority of pollination services. Future land use and crop production patterns may further increase the role of pollination services to UK agriculture, highlighting the importance of measures aimed at maintaining both wild and managed species
Money and happiness : rank of income, not income, affects life satisfaction
Does money buy happiness, or does happiness come indirectly from the higher rank in society that money brings? Here we test a rank hypothesis, according to which people gain utility from the ranked position of their income within a comparison group. The rank hypothesis contrasts with traditional reference income hypotheses, which suggest utility from income depends on comparison to a social group reference norm. We find that the ranked position of an individual’s income predicts general life satisfaction, while absolute income and reference income have no effect. Furthermore, individuals weight upward comparisons more than downward comparisons. According to the rank hypothesis, income and utility are not directly linked: Increasing an individual’s income will only increase their utility if ranked position also increases and will necessarily reduce the utility of others who will lose rank
Inhaled beclomethasone/formoterol in idiopathic pulmonary fibrosis: A randomised controlled exploratory study
Electronic spin precession and interferometry from spin-orbital entanglement in a double quantum dot
A double quantum dot inserted in parallel between two metallic leads allows
to entangle the electron spin with the orbital (dot index) degree of freedom.
An Aharonov-Bohm orbital phase can then be transferred to the spinor
wavefunction, providing a geometrical control of the spin precession around a
fixed magnetic field. A fully coherent behaviour is obtained in a mixed
orbital/spin Kondo regime. Evidence for the spin precession can be obtained,
either using spin-polarized metallic leads or by placing the double dot in one
branch of a metallic loop.Comment: Final versio
A non-pulsating neutron star in the supernova remnant HESS J1731-347 / G353.6-0.7 with a carbon atmosphere
Context: The CCO candidate in the center of the supernova remnant shell HESS
J1731-347 / G353.6-0.7 shows no pulsations and exhibits a blackbody-like X-ray
spectrum. If the absence of pulsations is interpreted as evidence for the
emitting surface area being the entire neutron star surface, the assumption of
the measured flux being due to a blackbody emission translates into a source
distance that is inconsistent with current estimates of the remnant's distance.
Aims: With the best available observational data, we extended the pulse period
search down to a sub-millisecond time scale and used a carbon atmosphere model
to describe the X-ray spectrum of the CCO and to estimate geometrical
parameters of the neutron star. Methods: To search for pulsations we used data
of an observation of the source with XMM-Newton performed in timing mode. For
the spectral analysis, we used earlier XMM-Newton observations performed in
imaging mode, which permits a more accurate treatment of the background. The
carbon atmosphere models used to fit the CCO spectrum are computed assuming
hydrostatic and radiative equilibria and take into account pressure ionization
and the presence of spectral lines. Results: Our timing analysis did not reveal
any pulsations with a pulsed fraction above ~8% down to 0.2 ms. This finding
further supports the hypothesis that the emitting surface area is the entire
neutron star surface. The carbon atmosphere model provides a good fit to the
CCO spectrum and leads to a normalization consistent with the available
distance estimates of the remnant. The derived constraints on the mass and
radius of the source are consistent with reasonable values of the neutron star
mass and radius. After the CCO in Cas A, the CCO in HESS J1731-347 / G353.6-0.7
is the second object of this class for which a carbon atmosphere model provides
a consistent description of X-ray emission.Comment: 6 pages, 5 figures, accepted for publication in
Astronomy&Astrophysic
Electrically driven spin resonance in a bent disordered carbon nanotube
Resonant manipulation of carbon nanotube valley-spin qubits by an electric
field is investigated theoretically. We develop a new analysis of electrically
driven spin resonance exploiting fixed physical characteristics of the
nanotube: a bend and inhomogeneous disorder. The spectrum is simulated for an
electron valley-spin qubit coupled to a hole valley-spin qubit and an impurity
electron spin, and features that coincide with a recent measurement are
identified. We show that the same mechanism allows resonant control of the full
four-dimensional spin-valley space.Comment: 11 pages, 7 figure
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