22,504 research outputs found
Cultivating Sustainable Coffee: Persistent Paradoxes
This chapter discusses the relationship and interconnections among changing the livelihoods of farmers, initiatives for sustainable coffee, and the production of shade-grown coffee. It examines the advantages and opportunities for farmers and producers engaged in coffee certification and diversification programs. The role of Fair Trade and organic networks in creating awareness of biodiversity conservation, the social and environment costs of coffee systems, and the need for supporting small farmers are also discussed. The methods to increase accountability and improve the efficiency of coffee cooperatives are presented in this chapter, as are the importance of understanding the sustainability initiatives and their implications for the regulators, along with the use of land patterns for coffee cultivation
X-ray Emission from SN 2012ca: A Type Ia-CSM Supernova Explosion in a Dense Surrounding Medium
X-ray emission is one of the signposts of circumstellar interaction in
supernovae (SNe), but until now, it has been observed only in core-collapse
SNe. The level of thermal X-ray emission is a direct measure of the density of
the circumstellar medium (CSM), and the absence of X-ray emission from Type Ia
SNe has been interpreted as a sign of a very low density CSM. In this paper, we
report late-time (500--800 days after discovery) X-ray detections of SN 2012ca
in {\it Chandra} data. The presence of hydrogen in the initial spectrum led to
a classification of Type Ia-CSM, ostensibly making it the first SN~Ia detected
with X-rays. Our analysis of the X-ray data favors an asymmetric medium, with a
high-density component which supplies the X-ray emission. The data suggest a
number density cm in the higher-density medium, which is
consistent with the large observed Balmer decrement if it arises from
collisional excitation. This is high compared to most core-collapse SNe, but it
may be consistent with densities suggested for some Type IIn or superluminous
SNe. If SN 2012ca is a thermonuclear SN, the large CSM density could imply
clumps in the wind, or a dense torus or disk, consistent with the
single-degenerate channel. A remote possibility for a core-degenerate channel
involves a white dwarf merging with the degenerate core of an asymptotic giant
branch star shortly before the explosion, leading to a common envelope around
the SN.Comment: 11 pages, 4 figures. Accepted to MNRA
Analyticity constraints for hadron amplitudes : going high to heal low energy issues
Analyticity constitutes a rigid constraint on hadron scattering amplitudes. This property is used to relate models in different energy regimes. Using meson photoproduction as a benchmark, we show how to test contemporary low-energy models directly against high-energy data. This method pinpoints deficiencies of the models and treads a path to further improvement. The implementation of this technique enables one to produce more stable and reliable partial waves for future use in hadron spectroscopy and new physics searches
On the and Photoproduction Beam Asymmetry at High Energies
We show that, in the Regge limit, beam asymmetries in and
photoproduction are sensitive to hidden strangeness components. Under
reasonable assumptions about the couplings we estimate the contribution of the
Regge pole, which is expected to be the dominant hidden strangeness
contribution. The ratio of the asymmetries in and production is
estimated to be close to unity in the forward region at the photon energy ~GeV, relevant for the upcoming
measurements at Jefferson Lab.Comment: 9 pages, 4 figure
Local mapping of dissipative vortex motion
We explore, with unprecedented single vortex resolution, the dissipation and
motion of vortices in a superconducting ribbon under the influence of an
external alternating magnetic field. This is achieved by combing the phase
sensitive character of ac-susceptibility, allowing to distinguish between the
inductive-and dissipative response, with the local power of scanning Hall probe
microscopy. Whereas the induced reversible screening currents contribute only
inductively, the vortices do leave a fingerprint in the out-of-phase component.
The observed large phase-lag demonstrates the dissipation of vortices at
timescales comparable to the period of the driving force (i.e. 13 ms). These
results indicate the presence of slow microscopic loss mechanisms mediated by
thermally activated hopping transport of vortices between metastable states.Comment: 5 pages, 2 figure
Functional Approach to Stochastic Inflation
We propose functional approach to the stochastic inflationary universe
dynamics. It is based on path integral representation of the solution to the
differential equation for the scalar field probability distribution. In the
saddle-point approximation scalar field probability distributions of various
type are derived and the statistics of the inflationary-history-dependent
functionals is developed.Comment: 20 pages, Preprint BROWN-HET-960, uses phyzz
Late-Time Circumstellar Interaction in a Spitzer Selected Sample of Type IIn Supernovae
Type IIn supernovae (SNe IIn) are a rare (< 10%) subclass of core-collapse
SNe that exhibit relatively narrow emission lines from a dense, pre-existing
circumstellar medium (CSM). In 2009, a warm Spitzer survey observed 30 SNe IIn
discovered in 2003 - 2008 and detected 10 SNe at distances out to 175 Mpc with
unreported late-time infrared emission, in some cases more than 5 years
post-discovery. For this single epoch of data, the warm-dust parameters suggest
the presence of a radiative heating source consisting of optical/X-ray emission
continuously generated by ongoing CSM interaction. Here we present
multi-wavelength follow-up observations of this sample of 10 SNe IIn and the
well-studied Type IIn SN 2010jl. A recent epoch of Spitzer observations reveals
ongoing mid-infrared emission from nine of the SNe in this sample. We also
detect three of the SNe in archival WISE data, in addition to SNe 1987A,
2004dj, and 2008iy. For at least five of the SNe in the sample, optical and/or
X-ray emission confirms the presence of radiative emission from ongoing CSM
interaction. The two Spitzer nondetections are consistent with the forward
shock overrunning and destroying the dust shell, a result that places upper
limits on the dust-shell size. The optical and infrared observations confirm
the radiative heating model and constrain a number of model parameters,
including progenitor mass-loss characteristics. All of the SNe in this sample
experienced an outburst on the order of tens to hundreds of years prior to the
SN explosion followed by periods of less intense mass loss. Although all
evidence points to massive progenitors, the variation in the data highlights
the diversity in SN IIn progenitor evolution. While these observations do not
identify a particular progenitor system, they demonstrate that future,
coordinated, multi-wavelength campaigns can constrain theoretical mass-loss
models.Comment: 10 pages, 6 figures, accepted to AJ (with comments
PTF11kx: A Type Ia Supernova with Hydrogen Emission Persisting After 3.5 Years
The optical transient PTF11kx exhibited both the characteristic spectral
features of Type Ia supernovae (SNe Ia) and the signature of ejecta interacting
with circumstellar material (CSM) containing hydrogen, indicating the presence
of a nondegenerate companion. We present an optical spectrum at days
after peak from Keck Observatory, in which the broad component of H
emission persists with a similar profile as in early-time observations. We also
present IRAC detections obtained and days after peak,
and an upper limit from ultraviolet imaging at days. We interpret
our late-time observations in context with published results - and reinterpret
the early-time observations - in order to constrain the CSM's physical
parameters and compare to theoretical predictions for recurrent nova systems.
We find that the CSM's radial extent may be several times the distance between
the star and the CSM's inner edge, and that the CSM column density may be two
orders of magnitude lower than previous estimates. We show that the H
luminosity decline is similar to other SNe with CSM interaction, and
demonstrate how our infrared photometry is evidence for newly formed,
collisionally heated dust. We create a model for PTF11kx's late-time CSM
interaction and find that X-ray reprocessing by photoionization and
recombination cannot reproduce the observed H luminosity, suggesting
that the X-rays are thermalized and that H radiates from collisional
excitation. Finally, we discuss the implications of our results regarding the
progenitor scenario and the geometric properties of the CSM for the PTF11kx
system.Comment: 15 pages, 8 figures, 3 tables; submitted to Ap
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