15,144 research outputs found
Astrometric Galactic maser measurements cross-matched with Gaia
Using the VLBA, the BeSSeL survey has provided distances and proper motions
of young massive stars, allowing an accurate measure of the Galactic spiral
structure. By the same technique, we are planning to map the inner Galaxy using
positions and velocities of evolved stars (provided by the BAaDE survey). These
radio astrometric measurements (BeSSeL and BAaDE) will be complementary to Gaia
results and the overlap will provide important clues on the intrinsic
properties and population distribution of the stars in the bulge.Comment: To appear in the Proceedings of the IAU Symposium No. 334:
"Rediscovering our Galaxy
Maser, infrared and optical emission for late-type stars in the Galactic plane
Radio astrometric campaigns using VLBI have provided distances and proper
motions for masers associated with young massive stars (BeSSeL survey). The
ongoing BAaDE project plans to obtain astrometric information of SiO maser
stars located in the inner Galaxy. These stars are associated with evolved,
mass-losing stars. By overlapping optical (Gaia), infrared (2MASS, MSX and
WISE) and radio (BAaDE) sources, we expect to obtain important clues on the
intrinsic properties and population distribution of late-type stars. Moreover,
a comparison of the Galactic parameters obtained with Gaia and VLBI can be done
using radio observations on different targets: young massive stars (BeSSeL) and
evolved stars (BAaDE).Comment: To appear in the Proceedings of the IAU Symposium No. 336:
Astrophysical Masers: Unlocking the Mysteries of the Univers
The Social Architecture of Local Food Tourism: Challenges and Opportunities for Community Economic Development
Local food tourismâculinary tourism with an explicit emphasis on local food systemsâis emerging as a âgreenâ model for community economic development. However, do local food tourism networks constitute a net gain to community economies in all contexts? This article explores that question through surveys and interviews with farmers, restaurateurs, and food tourists in three Wisconsin counties. Framing our discussion using the community capitals framework, we argue that economic benefits do accrue to communities from participation in these networks, but the net gains are ambiguous. Specifically, involvement in local food tourism networks increases stocks of social and human capital, deepens marketing opportunities for participating enterprises, and confers a price premium for food marketed as local. However, there can be significant transaction costs associated with participation, certain types of natural and cultural capital must prefigure successful execution, and restaurateurs levy significant power over farmers within the local food network. These tradeoffs demonstrate that growth in particular community capitals may not always be unequivocally good for communities
The Diverse Solar Phase Curves of Distant Icy Bodies. II. The Cause of the Opposition Surges and Their Correlations
We collect well-measured opposition surge properties for many icy bodies
orbiting the Sun (mostly from our own observations) plus for many icy moons,
resulting in a data base of surface and orbital properties for 52 icy bodies.
(1) We put forward four criteria for determining whether the surge is being
dominated by shadow hiding (SH) or coherent backscattering (CB) based on
readily measured quantities. The CB surge mechanism dominates if the surge is
color dependent, the phase curve is steeper than 0.04 mag/deg, the phase curve
shape matches the CB model of Hapke, or if the albedo is higher than roughly
40%. (2) We find that virtually all of our sample have their phase curves
dominated by CB at low phase angles. (3) We present a graphical method to
determine the Hapke surge parameters B_C0 and h_C. (4) The Kuiper Belt Objects
(KBOs) and Centaurs have relatively high surge amplitudes, B_C0 > ~0.5 and
widths with h_C ~ 3 deg. (5) We find highly significant but loose correlations
between surge properties and the colors, albedos, and inclinations. We
interpret this as young surfaces tending to have low surge slopes, high albedo,
and gray colors. (6) Nereid has its surface properties similar to other icy
moons and greatly different from KBOs and Centaurs, so we conclude that Nereid
is likely a nearly-ejected inner Neptunian moon rather than a captured KBO.Comment: Astronomical Journal, in press, 41 pages, 5 figure
Photospheric flux cancellation and associated flux rope formation and eruption
We study an evolving bipolar active region that exhibits flux cancellation at
the internal polarity inversion line, the formation of a soft X-ray sigmoid
along the inversion line and a coronal mass ejection. The evolution of the
photospheric magnetic field is described and used to estimate how much flux is
reconnected into the flux rope. About one third of the active region flux
cancels at the internal polarity inversion line in the 2.5~days leading up to
the eruption. In this period, the coronal structure evolves from a weakly to a
highly sheared arcade and then to a sigmoid that crosses the inversion line in
the inverse direction. These properties suggest that a flux rope has formed
prior to the eruption. The amount of cancellation implies that up to 60% of the
active region flux could be in the body of the flux rope. We point out that
only part of the cancellation contributes to the flux in the rope if the arcade
is only weakly sheared, as in the first part of the evolution. This reduces the
estimated flux in the rope to or less of the active region flux. We
suggest that the remaining discrepancy between our estimate and the limiting
value of of the active region flux, obtained previously by the flux
rope insertion method, results from the incomplete coherence of the flux rope,
due to nonuniform cancellation along the polarity inversion line. A hot linear
feature is observed in the active region which rises as part of the eruption
and then likely traces out field lines close to the axis of the flux rope. The
flux cancellation and changing magnetic connections at one end of this feature
suggest that the flux rope reaches coherence by reconnection shortly before and
early in the impulsive phase of the associated flare. The sigmoid is destroyed
in the eruption but reforms within a few hours after a moderate amount of
further cancellation has occurred.Comment: Astron. Astrophys., in pres
How universal is the fractional-quantum-Hall edge Luttinger liquid?
This article reports on our microscopic investigations of the edge of the
fractional quantum Hall state at filling factor . We show that the
interaction dependence of the wave function is well described in an
approximation that includes mixing with higher composite-fermion Landau levels
in the lowest order. We then proceed to calculate the equal time edge Green
function, which provides evidence that the Luttinger exponent characterizing
the decay of the Green function at long distances is interaction dependent. The
relevance of this result to tunneling experiments is discussed.Comment: 5 page
A point process framework for modeling electrical stimulation of the auditory nerve
Model-based studies of auditory nerve responses to electrical stimulation can
provide insight into the functioning of cochlear implants. Ideally, these
studies can identify limitations in sound processing strategies and lead to
improved methods for providing sound information to cochlear implant users. To
accomplish this, models must accurately describe auditory nerve spiking while
avoiding excessive complexity that would preclude large-scale simulations of
populations of auditory nerve fibers and obscure insight into the mechanisms
that influence neural encoding of sound information. In this spirit, we develop
a point process model of the auditory nerve that provides a compact and
accurate description of neural responses to electric stimulation. Inspired by
the framework of generalized linear models, the proposed model consists of a
cascade of linear and nonlinear stages. We show how each of these stages can be
associated with biophysical mechanisms and related to models of neuronal
dynamics. Moreover, we derive a semi-analytical procedure that uniquely
determines each parameter in the model on the basis of fundamental statistics
from recordings of single fiber responses to electric stimulation, including
threshold, relative spread, jitter, and chronaxie. The model also accounts for
refractory and summation effects that influence the responses of auditory nerve
fibers to high pulse rate stimulation. Throughout, we compare model predictions
to published physiological data and explain differences in auditory nerve
responses to high and low pulse rate stimulation. We close by performing an
ideal observer analysis of simulated spike trains in response to sinusoidally
amplitude modulated stimuli and find that carrier pulse rate does not affect
modulation detection thresholds.Comment: 1 title page, 27 manuscript pages, 14 figures, 1 table, 1 appendi
Eisenstein series for infinite-dimensional U-duality groups
We consider Eisenstein series appearing as coefficients of curvature
corrections in the low-energy expansion of type II string theory four-graviton
scattering amplitudes. We define these Eisenstein series over all groups in the
E_n series of string duality groups, and in particular for the
infinite-dimensional Kac-Moody groups E9, E10 and E11. We show that,
remarkably, the so-called constant term of Kac-Moody-Eisenstein series contains
only a finite number of terms for particular choices of a parameter appearing
in the definition of the series. This resonates with the idea that the constant
term of the Eisenstein series encodes perturbative string corrections in
BPS-protected sectors allowing only a finite number of corrections. We underpin
our findings with an extensive discussion of physical degeneration limits in
D<3 space-time dimensions.Comment: 69 pages. v2: Added references and small additions, to be published
in JHE
Where do graduates Develop their Enterprise Skills? The Value of the Contribution of Higher Education Institutionsâ Context
This study investigates the value of the contribution of HEIsâ context in developing graduates enterprise skills. HEIs are under pressure to develop more enterprising graduates, particularly with the increasing numbers of graduates seeking employment and the growing dissatisfaction of employers. This study explores where graduates develop enterprise skills through investigating the impact of HE and employment contexts on their development. The paper draws on a qualitative study in the social constructionist paradigm within the pharmacy context, where interviews were conducted with pharmacy academics and employers. Results show that ability to demonstrate skills in one context does not necessarily mean ability to demonstrate them in another since the development and demonstration of enterprise skills is impacted by the contexts in which they are developed and demonstrated. The study adds value by highlighting the significant role of both HE and employment contexts in developing enterprise skills, while emphasising that these skills become more transferable through exposure to more contexts
Physical States of the Quantum Conformal Factor
The conformal factor of the spacetime metric becomes dynamical due to the
trace anomaly of matter fields. Its dynamics is described by an effective
action which we quantize by canonical methods on the Einstein universe . We find an infinite tower of discrete states which satisfy the
constraints of quantum diffeomorphism invariance. These physical states are in
one-to-one correspondence with operators constructed by integrating integer
powers of the Ricci scalar.Comment: PlainTeX File, 34 page
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